Figure 1: 1990 Chevy Celebrity 3.1L

I got a distress call from a shop for a complaint of a hard starting when hot with a 1990 Chevy Celebrity with 3.1L engine (Figure 1). The old engine would run great when first fired up cold and had plenty of power, but as it warmed up it started to hesitate and run erratically. If it was shut off hot, it would be very hard to restart. The shop had already replaced the fuel pump, TPS, MAP sensor, and the PCM, but nothing seemed to resolve the problem. At this point the shop decided to call me in for a second opinion.

When I arrived, the engine was cold and it started up and ran with no problems present. I proceded to pull codes from the PCM and found a Code 15 (Coolant Sensor low) and a Code 33 (Manifold Air Pressure high) stored in memory (Figure 2). These codes were created by the shop when they were unplugging sensors to locate the cause of the problem. It is not uncommon to find codes in a system that are unrelated to the real problem — techs have created them during diagnosis. But it is still important to investigate them to validate if they were falsely set and then clear the codes to see if they return. The present codes must be cleared because there are certain controllers that may put the system in a default or back-up mode if they are not cleared from memory. Some systems may even place a default reading in the data parameter field dealing with a sensor error code that could throw you for a loop. It’s interesting that all this is relevant even on a 21-year-old car.

Figure 2: ECM trouble codes stored in memory

Figure 3: ECM data parameters

Figure 4: Viewing data parameters in graphing mode

The main focus of the PCM is to achieve fuel control, and when it cannot meet its goal fine tuning the fuel requirements using the constantly moving Integrator, it will quickly kick in Block Learn to make a major adjustment in fuel delivery. When I released the throttle the PCM reverted to its stored Block Learn value of 155 and then started to add more fuel by moving the Integrator as high as 180 again. The O2 sensor still could not reach a threshold above 600 mV. This engine had a fuel starvation problem that the PCM could not overcome.

Figure 5: Checking fuel pressure with a guage

I kept it simple realizing that all the computer parameters were within their ranges. This had to be a fuel delivery issue such as low fuel pressure, or even clogged injectors. I next placed my fuel pressure guage on the engine (Figure 5) and saw that the fuel pressure was within specifications at about 36 psi, but I did not know if the PCM was doing its job of properly delivering the pulse width needed to keep the injectors open long enough for sufficient fuel delivery. Looking at a fuel pulse-width parameter on a scan tool is not a true indication of actual fuel delivery, but rather the pipe dream the PCM hopes to deliver if the injector driver is working properely. This could only be further diagnosed using an oscilloscope.

This PCM controlled the injectors using two separate drivers each managing two sets of three injectors each in group-firing format. I placed my scope leads on each injector driver circuit and viewed both voltage patterns in superimposed format on my scope screen (Figure 6). Both patterns seemed okay at first glance, but a closer look revealed that both injector patterns were elevated at about 3000mV and the PCM was unable to properly pull the injector field coil circuits fully to ground. This could be an indication of a poor PCM ground, a bad injector driver, or a shorted injector circuit. The voltage trace only gives you a portion of the picture and you really need a current waveform to see what’s going on.

Figure 6: Scope checking the voltage trace of both injector banks

Figure 7: Installing 2 current probes at the ECM connector to check current at each injector bank

I next placed two current probes on the injector circuits so I could superimpose both injector patterns on one screen. This I did at the PCM, which was located at the right front engine compartment (Figure 7). As I was looking at the current waveforms of both injector banks, I immediately saw the problem that was creating the lean condition (Figure 8). One bank of injectors was pulling close to 13 amps, while the other bank pulled only about 3.5 Amps. These were high-impedance injectors, and normally required about 900 mA of current each, so one bank of injectors must have had at least one partially-shorted injector coil causing the PCM to limit both banks to a predetermined grounding threshold to control injector current. The end result was a lean fuel output.

Figure 8: Scope checking the current trace of both injector banks

Figure 1: 2000 Toyota Solara

I was called in to a shop for a MIL-on (Malfunction Indicator Lamp, a.k.a. “CEL” for “Check Engine Light”) situation in a 2000 Toyota Solara with the 1MZ-FE engine (Figure 1). The shop had replaced two air/fuel ratio sensors, but the MIL came back on after the vehicle was delivered to and driven by the customer. The tech had checked all the fuses, but could not locate the source of the circuit problem affecting the sensors so he wanted a second opinion to get this monkey off his back and down the road. It was bad enough that the shop had replaced parts that were not needed, but now the customer was putting pressure on the shop to get the car fixed, or he wanted his money back. We’ve all been down this road and it’s not a good feeling because you know whatever turns up is going to have to be fixed at your expense and chalked up to the never-ending automotive learning curve.

When I arrived at the shop, I noticed that the MIL was on so I opted to hook up my Toyota Techstream scan tool to see what codes were stored in the PCM. I selected “Trouble Codes” from the menu and found five codes stored in memory (Figure 2). Two of the codes, P1130 and P1150, were related to a range/performance issue with both upstream air/fuel ratio sensors. The next two codes, P1135 and P1155, were related to a heater circuit malfunction in both of those sensors. The fifth code P0125 (Insufficient Coolant Temperature for Closed Loop Fuel Operation) is one that takes many scan tool gurus down the wrong diagnostic path. They often mistake this as an indication of a bad engine thermostat when in reality it is letting you know that the air/fuel ratio sensor can’t reach its proper operating temperature due to a heater circuit problem.

Figure 2: Codes retrieved in ECM using the Toyota Techstream scan tool

Looking at the main four air/fuel ratio sensor codes, you need to divert your attention to heater circuit faults because if one is present range/performance codes will always be set as a secondary fault. If you think about it for a moment, you’ll realze that it’s not very likely that two A/F sensors would go bad at the same time, or even two heater driver circuits. It’s much more likely that something common to both heater circuits is at fault, such as a power feed source. Streamlining diagnostics like this cuts your chances of taking the wrong diagnostic path, so it’s important to use some “street smarts” when you approach a problem. It becomes a matter of automotive forensics to sift through the information you’ve gathered from your tests to see what’s really pertinent to the problem, then to apply logic.

Mode 6 is a scan tool feature that isn’t used by techs in the field nearly as often as it should be. This is mostly due to the unfriendly user interface that most scan tools, including factory units, provide. Toyota, however, has done a phenomenal job making things easier through hyperlinking. You go to the “Monitor” selection menu and there you will view all the monitors with their pass or fail status (Figure 3). Notice how the thumbs-down sign for O2 heater failure instantly draws your attention with a universal language. Click on the thumb and it will hyperlink to Mode 6 test results that are easy to read (Figure 4). By looking at these readings you can see that both upstream A/F sensor heaters failed to achieve the minimum current threshold of 2.492 amps — their test value was at 0.221 amps. By viewing the threshold information, you can conclude that both heater circuits pulled almost no current, which is an indication of an open circuit for both banks.

Viewing the OBDII Monitors using the Toyota Techstream scan tool

Figure 4: Viewing the Mode 6 results of the O2 sensor heater Using the Toyota Techstream scan tool

This scan tool is hooked up live to the Toyota website through a subscription, so all I needed to do is use the “TIS Keyword” menu selection, which took me directly to Toyota’s website search engine. By placing the heater code P1135 in the keyword window, I was able to do a full search of the Toyota website and be directed to linked information to help me further my diagnostics (Figure 5). I clicked on the Repair Manual link for the code and it hyperlinked me to all the information I needed to perform my diagnostic tasks (Figure 6). You’ll notice the simplified layout of the DTC description, followed by circuit description, wiring diagram, and inspection procedure. The information on this page listed the code as two-trip detection logic and provided a maximum 8.0-amp or minimum 0.25-amp threshold for code setting.

Fig 5: Search results using the Toyota TIS website for trouble code information

Figure 6: Repair manual information for code P1135

Figure 7: Hyperlinked wiring diagram of the O2 heater circuit

Figure 8: Back probing the O2 heater relay to check contact feed to O2 heaters

I used the hyperlink DI-225 under “Wiring Diagram” and was linked to an isolated diagram of the heater circuit (Figure 7). By power-flow checking the diagram, you can see that power feed to the heating elements is supplied through the A/F heater relay contacts from an A/F heater fuse. I located the relay in the engine compartment relay box #2 and turned the box over to backprobe the relay contacts (Figure 8). The test light lit with the key on indicating that power was being supplied to wires leading to the sensors’ heaters. I next unplugged the Bank #2 A/F sensor connector located at the back of the engine to test it for power and found nothing there (Figure 9). There was an open circuit between the relay panel and the A/F sensor connector.

Figure 9: Testing the B2S1 O2 heater connector for power supply

When looking for an open circuit, you need to find out where the circuit begins and where it ends. Then, try to visualize how the circuit is routed — it’s almost like using X-ray vision. Next, find an accessible midpoint. This location will help you to determine if the problem is forward or backward of the area you have chosen. Start homing in on the open by tapping into the circuit with a test light to validate power feed. The midpoint I chose on this vehicle was the battery tray because the harness ran under the battery, then towards the rear of the engine where it was supposed to feed the bank #2′s A/F sensor connector.

Figure 10: Open O2 heater circuit under the battery tray

When I removed the battery and battery tray, I immediately noticed a crushed black wire housed in a conduit that was unplugged. It seemed to fit the description of a black wire that fed thesensor’s heater circuit. I decided to plug it back into a mating connector located under the left front fuse/relay panel (Figure 10) and restored 12V to the vehicle by using a jumper box so I could recheck the circuit. Once I did this, power appeared in the sensors’ heater circuits. It was like hitting the lottery. What are the chances of finding a connector that someone left unplugged, buried, and crushed under a battery tray?

It makes you wonder about other techs/mechanics in the field and how they can be so incompetent as not to remember to put something back the way they found it. This situation seems to be becoming more common with all the distractions around us while we work. Maybe the tech was returning a Tweet or updating his Facebook account. Who knows? We can also lose our focus and mindset when working on cars today because of time pressure from either the boss or the flat rate. Thanks to OBD II systems and the comprehensive tests they perform on modern cars, the onboard monitors usually won’t let a vehicle drive more than three roads trips before the MIL is lit. But what bothers me is how a job like this always winds up in another shop that had nothing to do with the prior repair. Perhaps this is a job-security feature built into our business to keep us going. Hope this one hits home for you — take it slow!

Figure 1: 2006 Honda Civic

I received a distress call from a body shop for a complaint of a no-start on a 2006 Honda Civic. The shop had just finished working on the vehicle and decided to detail the car for the owner as a courtesy. The detail guy loved his tunes so he decided to leave the ignition key on and crank up his favorite station while he was working. I could only envision this guy dancing around the car singing “Working at The Car Wash” and having a good time as he was fully unaware of the accessory position that car manufactures use to limit battery drain. When the detailer was all done with the vehicle he went to crank the engine and heard the famous slow dragging sound of the engine followed by a click-click-click. We have all been here before and a simple jump start with a battery charger on boost mode or the use of a jumper box always gets us back on track. The jump start attempted on this vehicle only provided an extended good crank with a no-start. The car was running prior to the battery going dead and now the shop was married to a no-start condition.

Figure 2: Instrument panel showing green security key

Figure 3: Close up view of Immobilizer Module & Antenna assembly

When I arrived at the shop I got in the car and attempted to start it. It cranked over fine, but wouldn’t fire. I did notice one thing the body shop had overlooked. There was a green key icon flashing on the instrument panel (Figure 2), indicating that that vehicle was immobilized. This Honda uses an immobilizer receiver and control unit assembly mounted on the ignition lock housing (Figure 3). It has a built-in antenna ring that mounts directly around the key hole to read the chip embedded within the immobilizer key. The key for the car was a correct black Honda key and not a gray valet key with limited use, but I was puzzled as to why the green key on the dash panel was flashing. I know from experience that if the PCM was to be inoperative and the immobilizer unit lost communication with it, then the immobilizer unit will flash the green key icon.

Figure 4: Performing ALL DTC code retrieval using Honda HDS scan tool

I hooked up my Honda HDS scan tool and performed an All DTC Check to see if there were any trouble codes on board and to verify that the PCM was functioning ( Figure 4). I was very surprised to see no codes in memory and that the PCM was responding because I was hoping to find something to give me direction. I just sat there for a moment thinking about what could have gone wrong. I can tell you that the worst thing you can ever do on the cars of today is drag a battery down really low on a slow crank because it can allow many controllers on board to lose learned functions. This is why certain manufactures such as BMW will not allow the vehicle to crank if the battery voltage is too low. My guess at this point was that the key’s learned memory might have been lost.

Figure 5: Immobilizer Menu view using the Honda HDS scan tool

At this point, I decided to relearn the key so I went into the Immobilizer menu (Figure 5) of the Honda HDS scan tool and selected “Add and Delete Keys”. The Honda scan tool cautions us not to use a key with “T5″ stamped on the metal blade (Figure 6) .This is a clone key without its own identity and can only be used in a key duplicator machine used by your local locksmith. This key was a true Honda key, not a T5, so I went through the procedure to learn the key, but every time I tried to complete the procedure I received the error message “Immobilizer System is not Normal” (Figure 7). The HDS provides a help screen for this error message and directs your attention to check the PCM for a registration issue or communication issue with the immobilizer control unit. Okay, so maybe the PCM lost its alignment with the immobilizer due to a low battery condition. A lot of antitheft systems use a separate controller that will work in conjunction with the main Engine Control Module to control engine shutdown. Some systems block starter operation, while others do not, and some may even prevent spark and fuel pulse at the same time from occurring. I prefer the systems that provide a start and stall condition so at least you know you’re definitely dealing with an anti-theft issue.

Figure 6: Caution screen alerting attention to using clone keys

Figure 7: Immobilizer error screen view using the Honda HDS

So now I went back to the immobilizer menu and selected “Replace ECM/PCM” to see if registering the PCM would resolve the problem. I went through the whole procedure and again the same error message “Immobilizer System not Normal.” I did not want to start playing Russian roulette here with automotive parts, but I’ve done many of these Honda anti-theft systems and whenever I’ve come across this error message it has always been a new PCM/Immobilizer Control unit that was installed or a wrong key type being used. I next went ahead and tried to realign the Immobilizor Control unit as a last effort, but again had the same message. Now it was time to do some soul-searching in hopes of finding a resolution for for my dilemma.

Figure 8: Honda service bulletin 06-036 relating the vehicle failure

I started by looking through a lot of service bulletins in my AllData system, and finally came across one that seemed to fit. It was titled “Immobilizor Indicator Is Blinking, Engine Won’t Start” (Figure 8). This bulletin only pertained to 2006 Honda Civics and states that this problem will occur on this particular vehicle after a battery recently went dead and the engine was jump started. Honda recommends replacing the under dash fuse/relay panel ECU called the MICU (Figure 9) due to its loss of the immobilizer IMOES code. Apparently, this anti-theft system has another controller in the mix that is not commonly used on other models. I might have seen the MICU within the Honda immobilizer menu on certain year/models before, but never directed my attention toward it. It just seemed crazy to have a shop have to purchase a brand-new electronic fuse panel from just a battery going dead.

Figure 9: Close up view of the under dash fuse/relay box (MICU)

Then I started thinking. You know, I’m a gambler at times and it’s on the immobilizer menu so why not try to realign this MICU unit back into this so-called anti-theft network party gone wild. I now went back to the vehicle and from the Immobilizer menu I selected “Replace MPC/MICU/IMOES” and followed the realignment procedure. I got all the way to the last step without any error messages and the car starts up and runs. Okay, now what? I have a car that runs and a shop that’s beaming with joy. I took a step back to understand what was going on here. My guess is that Honda may be having a problem with its 2006 Civics that can’t keep information in the volatile memory of the MICU unit if the battery goes too low. So the company’s resolution is to replace the unit under a quiet service bulletin without issuing a recall. What a turn of events! My only hope is that this one keeps you from jumping the gun on replacing unneeded parts and teaches you a valuable lesson to not let battery voltage levels drop too low.

Figure 1: 2007 Jeep Grand Cherokee

Figure 2: Powertrain Control Module located at right rear of engine compartment

I was called to a shop to program a new Powertrain Control Module on a 2007 Jeep Grand Cherokee (Figute 1). The shop diagnosed the Jeep and made the decision to purchase a new PCM to resolve a no-start situation. Reprogramming has become a common practice for me these days because a lot of shops do not want to get involved with the procedure. It may be due to costly subscription fees or just the liabilities involved when programming a controller. If you don’t know what you’re doing, or are just not careful enough you could be the proud owner of a new or rebuilt computer. So, sometimes it may be easier for a shop owner to hire my company for these services.

Figure 3: Topology view of onboard controller using the Chrysler WiTech softwareTopology view of onboard controller using the Chrysler WiTech software

I arrived at the shop and plugged in the old contoller first to read software information about the module so that I could select the proper software I needed on the Chysler website (Figure 2). I placed my Chysler StarMobile interface on the truck and booted up the WiTech software program to “topology” view with the vehicle online with Chrysler’s website. This view is live and provides a lot of information for the working technician with just with one glance at the screen. The controllers are all grouped by different types of networks. Blue lines indicating CAN B, black lines indicating CAN C, gray lines indicating a path to a controller that is not actually on the car, and red lines indicating a dead link to an inoperative controller (Figure 3).You will also notice that any controllers with codes are highlighted in yellow and without codes in blue. If any controllers are in red, they are considered inoperative and off the network. If you look closely, you can see a small green lightning bolt icon on certain controllers indicating that a flash file is available. This is the way a scan tool should be built to really make things easier for the technician.

Figure 4: “U” codes stored in memory

Figure 5: Highlighting the circuit diagram for an easier view of the power and ground feeds

The topology view showed that the PCM was inoperative and I could not communicate with it. The shop techs had the same problem when they hooked up their scan tool, so after performing some checks on the vehicle they determined that the PCM had internal issues. I plugged in the new controller and it didn’t respond, either. The shop had also plugged in the new PCM, but they thought it had to be programmed before it would communicate. I explained to them that even though no software is loaded in the new PCM, it still had a boot file in it to allow it to communicate with the scan tool. There was no way I could do the programming without communication with the PCM. When I minimized the topology screen to view the codes below it, there were a lot of “U” codes stored in other controllers in the network because of the PCM failure (Figure 4). The shop had made a bad decision to condemn the old PCM for not communicating with their scan tool. This vehicle had a wiring problem and I would have to pull some diagrams to power-flow system operation prior to my diagnosis.

Figure 6: Highlighting the circuit diagram to follow the PCM ignition feed back to fuse #24

Figure 7: Validating power feed at fuse #24 at the left side lower fuse panel

I used Mitchell On Demand to pull a diagram of the PCM (Figure 5). I color-coded the grounds at terminals #9 and # 18 with green , battery feeds at terminals #10 and #29 with red, and ignition feed at terminal #11 with purple. This coloring process makes it easier to read a diagram by isolating the circuits you need to check and mentally flows circuit operation so that you grasp it better. I backprobed the PCM terminals with a test light and found that there was no ignition feed at terminal #11. I printed out another diagram (Figure 6) and followed the ignition feed circuit back to Fuse #24 located in the junction box at the left side of the lower dash. I checked the fuse with a test light and there was no power on either side of the fuse with the key on (Figure 7). I now needed to find out how fuse #24 got its power, so I next printed out another diagram (Figure 8) and followed the #24 fuse feed all the way back to terminal #9 of the C2 connector within the fuse panel housing highlighted in purple.

Figure 8: Highlighting the circuit diagram to find the source feed for fuse #24

I placed my test light on the #9 terminal pin at the C2 connector of the left side junction box and found that the ignition feed going into the panel was okay (Figure 9). The culprit was a bad fuse panel with an open internal feed circuit. The fix here was to replace the entire fuse panel. At this point the only choice I had was to run a temporary feed line to the PCM to validate my findings to see if the car would run and to make sure there weren’t any more problems at hand. I jumped out the ignition feed to the PCM with a power source (Figure 10) and the car started and ran fine. I then finalized the diagnosis and went back to my topology view to do a health status on the system (Figute 11). I could now see that the TCM and the ABS modules were also up and running because they most likely shared the same ignition feed that was missing. I could also see that there are flash files available for the PCM and the TCM if the owner of the vehicle decides to do some upgrades.

So, the car was running and there was no need for the new PCM that the shop purchased. Parts suppliers usually won’t take back an electrical part, so now the shop owner faced an ethical dilemma. Should he be honest, eat the unnecessary expense and chalk it up to a learning experience? Or, should he have me program the new control unit and bury the whole mess without the owner of the vehicle ever knowing what happened? After all, the customer only wants to see the car running no matter what it takes. I know we’ve all been there, and it is definitely a test of character. How well will your conscience let you sleep at night?

The lesson here is that while the occasional PCM will fail, it behooves you to be absolutely certain that everything it needs to function is available before you spring for the expense of replacing it. I hope this one hits home with a lot of my readers to always take step back in your diagnostics and make sure you’re seeing the big picture.

Figure 9: Validating ignition switch feed into the fuse panel junction block

Figure 10: By passing fuse #24 to power up the PCM

Figure 11: Validating the temporary fix by revisiting the topology view

Figure 1

A shop owner called me in on a complaint of erratic engine operation in a 2003 Saturn View with the 3.0L engine (Figure 1). He stated that the car would immediately start up and run fine with no problems at all. It even had plenty of power. That is, until you applied the brakes — then, it would begin to run rough and stall. When the trans was placed in Drive or Reverse, it would do the same thing, but when placed back into Park it would run fine again. It didn’t matter if the engine was cold or hot, but only if the vehicle was put into gear with your foot on the brake pedal. At first, this seemed like your typical brake booster failure, but it led me on a wild goose hunt!

The techs had done their homework by looking at many data parameters to see if anything changed from the time the vehicle was placed in Drive from the Park position. They discovered that the fuel trims were increasing to accommodate a lean condition. At this point, they believed that the brake booster was leaking due to the fact that the problem only occurred with your foot on the brake pedal. They pinched off the vacuum line to the brake booster, but the problem still prevailed. They next decided that the brake switch was the only correlation to stepping on the brake pedal and having an engine-running issue, so they removed and unplugged the brake switch. Once this was done the vehicle no longer experienced a problem when the brake pedal was applied. The shop had found the culprit, but they were confused as to what the brake switch had to do with an engine problem, so they called me in for technical assistance.

When I arrived at the shop, I had the technician show me the problem. He reinstalled the brake switch and started the engine, which ran very smoothly without any problem. Then, as soon as he stepped on the brake the engine started to surge and run erratically. He removed his foot from the brake pedal and the car ran fine. I stood there in disbelief because I have never seen anything like it. I thought it was some kind of practical joke the shop was playing on me, but it was for real. There definitely was a connection between latching the brake switch and having the car run poorly.

Figure 2

Figure 3

Figure 4

I hooked up my EASE scan tool to view some basic parameters such as rpm, coolant and air temp, mass air flow and throttle position (Figure 2), and everything seemed to be within range with my foot off the brake pedal. When I placed my foot on the brake pedal, I didn’t see any drastic changes in any of the parameters to point me in a sensible diagnostic direction. The shop mentioned to me that the fuel trims were changing when the brake pedal was being applied, so I decided to warm up the engine to take a look at it myself. I placed the long-term and short-term fuel trims in a graphing mode using one screen on the Escan, then placed both upper O2 sensors in a graphing mode on another screen. I watched the O2 sensors and fuel fuel trims with the engine idling and all seemed okay (Figure 3). When I stepped on the brake pedal, however, both O2 sensors went lean and the short-term fuel trim maximized to positive 25% without the PCM achieving any fuel control at all (Figure 4). This could be seen by viewing the flat line in both O2 signals that stayed near zero. As soon as I took my foot off the brake pedal, both O2 sensors hung at close to 800 mV due to the added fuel needed to overcome the prior lean problem. The PCM immediately went into fuel control by decreasing the fuel trim to about negative 10% to achieve O2 switching.

Figure 5

The engine was running very lean with my foot on the brake pedal, and the PCM just could not add enough fuel to overcome the condition. The only major contributors to fuel delivery on this system would be the MAF sensor and the fuel pump. I didn’t see a major change in the MAF reading on the scan tool as I put my foot on and off the brake pedal, so I decided to check the fuel pump output with a pressure gauge. At idle with my foot off the brake pedal, the pressure was within specifications at about 50 psi (Figure 5), but as I applied the brake pedal it dropped to about 20 psi ( Figure 6). This was why the engine went lean and the PCM increased the fuel trim counts on both banks. The only correlation I could put together at this point was that when my foot was on the pedal, the brake lights were being energized, so there had to be a shared ground or power feed with the fuel pump that was being overloaded. I was now on a diagnostic blitz mission because I had found the cause of the seemingly mysterious problem, but I needed to isolate the specific location of the defect. It was all about fuel pump wiring.

Figure 6

I went directly to the fuel pump feed wires under the vehicle and I had the tech apply the brake pedal while checking the power and ground feeds to the pump. I discovered a weak ground for the fuel pump. I followed the ground wire, but it seemed to travel back into the car. I didn’t want to waste a lot of time just looking around and hoping and poking — I needed to know exactly where the pump ground resided. This is where an information system that will show you what grounds are shared and where to locate them in the vehicle comes in handy. So, I went to my Mitchell Repair Information system to pull up a diagram of the fuel pump circuit. It labeled a pump ground #G403 located at the “right rear corner of the vehicle” (Figure 7). I also pulled a diagram of the brake lights and discovered that there was a common ground splice pack #G403 located in the “right rear of storage compartment.” I appreciated this more precise location description because “right rear corner” did not specify inside or outside of the vehicle. Then again, it was only a label on a diagram and not a ground location feature, which I would have used next within the program.

Figure 7

Figure 8

Figure 9

Figure 10

I opened the hatch and pulled back the rug at the right rear and found a broken ground splice (Figure 8). There was no direct fuel pump ground feed to the body of the vehicle, but rather a ground that was supposed to back-feed through this broken splice into the harness. Looking at a similar splice in the left rear cargo compartment gives you an idea what a good splice connection should look like (Figure 9). What was amazing to me was how the fuel pump motor back-fed through that splice to achieve enough of a ground to run at all. If any shared circuit on that splice suddenly needed a ground when the brakes were applied, there was just not enough to go around. This was why the fuel pump slowed down and put out less fuel pressure whenever the brake lights were energized.

This was a crazy problem because it was so hard to believe that a brake switch could take down a vehicle. At first it made my mind wander and draw a blank because stuff like this just doesn’t fit the pattern of normal diagnostics. It was exciting in the end to nail the culprit, and my only hope is that you can walk away learning something from this story.

Figure 1: 1987 BMW 735i

I was called to a shop for a no-start on a 1987 BMW 735i (Figure 1). It was towed in — no spark and no injection pulse will do that. The techs tried replacing parts that they felt were common pattern failures in this particular vehicle.This included a crank sensor, cam sensor, and even a used PCM. They had obviously tried to gather information on the operation of the fuel injection system — they were sifting through a big pile of printouts (Figure 2). They were very limited on diagnostic tests, however, because this car had no diagnostic connector for pulling codes or using a scan tool view the datastream, so it was hard for them to get a sense of direction. They finally decided to call me in for technical assistance.

Figure 2: Printed vehicle info left on seat

This was definitely old-school technology and did not even have OBD I. I could see it was going to give me a run for my money because without datastream or trouble codes I was going to have to spend some time reading wiring diagrams and trying to understand how to perform pinout checks directly at the PCM connector to guarantee complete tests of each computer circuit. I was also going to have to think about voltage values of sensor signals and the different thresholds they achieve under many different operating conditions. This is where a good scope or a graphing multi-meter comes into play because certain sensors create fast signal outputs that would need to be viewed as a waveform pattern over time to validate their integrity.

Figure 3: Color flow diagram of ECM wiring

I needed to lay out a complete diagnostic routine for testing the pins at the Powertrain Control Module, so I printed out a diagram and started color coding it so I could mentally flow the circuits required to achieve spark and injection pulse (Figure 3). I applied a color-coding method I have been using for many years to help me relate to computer circuits. I traced all grounds with green, battery feed with orange, and ignition feed with pink. I then traced the dynamic sensors such as those for crank and cam position with yellow, and, lastly, the driver circuits such as ignition coil and injectors with blue.

To make things easier, I isolated all the wires I needed to check by locating them within the PCM connector (Figure 4). Before I got too technical and started checking dynamic sensors and driver circuits with a scope, I decided to keep it simple by first checking the PCM powers and grounds with a test light. I wanted to perform a static test to validate whether the PCM was getting what it needed to keep itself alive and breathing with the key on. This is a step very few techs ever bother to do prior to jumping into elaborate testing procedures. The grounds at pins #5, 10, 16, 17, and 19 all illuminated the test light, but this only validated that there was enough of a ground to operate a 300 mA draw on a testlight bulb, or the under-100 mA draw of a PCM at rest with the key on, engine off. Remember, while cranking, a coil driver within the PCM can draw as much as four to six amps, so the valid dynamic test would be to check voltage drop from the negative side of the battery to all PCM grounds while cranking with the PCM harness connected and using a limit of not more than 300 mV.

Figure 4: Isolating ECM circuits to be tested

Figure 5: Checking for ECM power feed

I now moved on to the power feed checks and found that there was battery voltage at pin #18, no illumination of my test light at pin #35 for ignition feed (Figure 5). I had to trace out another part of the wiring diagram to determine what circuit was responsible for sending power to the PCM with the key on (Figure 6). I followed pin #35′s wire on the diagram and it led me to a main PCM relay located in the right rear of the engine compartment. The relay contact got the same battery feed as PCM pin #18, and it illuminated my test light. On the relay coil side there was a good, constant ground, but there was no power (Figure 7).

Figure 6: Color flow diagram of ECM relay

I temporarily hot-wired the relay coil, cranked the engine, and it started. As soon as I pulled power away from the relay coil, it cut out and wouldn’t re-start. Okay, so now I found the essential problem, but I needed to backtrack some more to see where this power feed came from. The diagram labeled the power feed as coming from a source called “OBC relay box.” I was not familiar with this component, so I had to take a crash course on what this device was all about because I was not you’re a BMW guru, but rather a generalist who learns on the go.

Figure 7: Checking ECM relay coil feed

After doing some digging in my information systems, I found that there was an “On Board Controller” in the center of the dashboard. It had a multi-function control panel to the right of the heating and air conditioning panel that displays date, time, miles per gallon, and also allows the driver to enter a programmable four-digit access code to start the car (Figure 8). This was an early security system that disabled the vehicle once activated by the driver through this panel. The system was also designed to default to theft mode if the battery ever went dead, and display the word “CODE” in the panel. Once the battery is restored, the prior access code would no longer be valid and a new code would have to be set up through a series of steps.

Figure 8: On Board Controller panel at center dash

The owner tried to enter a new code several times before having the car towed, but it still wouldn’t start. The shop allowed the battery to drain a few times, which caused the OBC panel to go into theft mode. I was successful in programming a new code into the system, but the OBC unit still wouldn’t send ignition feed to the PCM relay coil. I pulled out the OBC device and did some power and ground checks on it, but everything tested okay. I did some further research and what I discovered was that BMW had issues with this panel. So, at this point it came down to the decision of whether to replace the panel, or simply bypass the relay driver coming from the panel and provide a direct ignition feed to the PCM relay coil. The shop alerted the owner of my findings, and he decided to have us bypass the panel to get the car back on the road. He could always decide later if he wanted to spend the money to re-enable the feature.

This was an interesting case that ended with a simple fix. There was no scan tool to hook up to this car, nor a need to use a scope. It just took a basic understanding of what a computer needs before it can operate an engine. It is important prior to testing any onboard controller to power-flow a system diagram so that you become familiar with how its circuits are laid out, and all the components involved. The game plan always starts on paper. Then you home in on the circuits you need to check. Always do this at the PCM because it’s the only way to guarantee that you’re checking all the circuits fully.

Figure 1: 2004 Nissan Pathfinder

I was called in to a shop for a complaint on a 2004 Nissan Armada (Figure 1). The MIL (or CEL, if you prefer) was on, and there was a lack of throttle response. The shop pulled trouble codes from the PCM pertaining to the accelerator pedal sensor and decided to replace the accelerator sensor assembly. This was not a good decision on their part because the problem was still there to haunt them. Now that they had put a part in the car they couldn’t very well return it unfixed, so they had essentially married. There was no turning because if you decide to turn the job away without resolving the problem, you can’t expect the owner of the vehicle to pay for any parts used in the attempted repair. That would be a nasty automotive divorce that could empty your pockets, not to mention costing you a customer who would have to look elsewhere. At this point, the garage called me in to get a second opinion.

Figure 2: Current ECM codes in memory

Figure 3: APP Sensor located at gas pedal

When I arrived, I attached my Nissan Consult III to the truck and pulled codes P2122, P2129 and P2138 (Figure 2), which were current. These codes dealt with the accelerator sensor that was located on the gas pedal. This is a dual potentiometer that provides the Powertrain Control Module with input on the position of the gas pedal. Both potentiometers are supplied with a separate five-volt reference and ground. The grounds are braided around each sensor signal line to cancel out noise (Figure 3). I used the scan tool to view both sensor signals at closed throttle with the key on/engine off (Figure 4) and noticed that accelerator sensor #1 was at 0.01 volts while accelerator sensor #2 was at 0.81 volts. Then I moved the accelerator pedal to the floor and accelerator sensor #2 displayed 4.40 volts while accelerator sensor #1 never changed (Figure 5).

Figure 4: APP Sensor readings at closed throttle

Figure 5: APP Sensor readings at wide open throttle

Figure 6: APP Sensor #1 Ref Voltage reading at ECM

The only way accelerator sensor #1 could be low was if the sensor had an open or shorted five-volt reference feed from the PCM, or an open or shorted signal line going back to the PCM. At this point, I decided to get my Power Probe out to do some simple checks at the accelerator sensor. I checked both five-volt reference feeds at the accelerator sensor first and found 0.2 volts at sensor #1 (light blue wire). I had to prove this circuit out, so I went directly to the PCM connector. The reading at there was also 0.2 volts (Figure 6), but I wasn’t sure if this was a shorted circuit to ground, or a lack of five volts coming out of the PCM. To be certain, I placed my test light on sensor #1′s feed circuit while it was connected to the positive side of the battery and the test light lit up (Figure 7). Keep in mind never to use a test light on a good working reference voltage feed line because the high current draw of the test light bulb could damage the internal circuitry of the PCM. The line was already low, so there was no chance of creating any damage if it were shorted to ground or open within the PCM.

Figure 7: APP Sensor #1 Ref Voltage circuit shorted to ground

Figure 8: APP Sensor #1 Ref Voltage circuit cut-Short remains

Now that I’d determined that the circuit was shorted to ground, I had to validate whether the short was internal or external to the PCM. So, I cut the wire at the PCM leading back to sensor #1 and found that the short circuit remained (Figure 8). This had to be a bad PCM because the short was now found to be on the PCM side. I advised the shop to get a used PCM just to keep costs low, and that I would be back to program it once they were able to locate one. I left feeling pretty good with my final diagnostic decision, so I moved on to the next shop.

Later in the week, the shop called in the morning asking me to program the used computer, so I went back there later in the day. I soldered the wire I had cut and paired the used PCM to the security system so the car would start. After it ran for a few seconds, the MIL came back on. This was not a good development because suddenly I was feeling the double marriage thing!

Figure 9: Diagram of 5 Volt Ref Voltage feeds from ECM

I switched my Nissan Consult III from security mode to scan tool mode and rechecked the codes. The same codes came back and I was no further along than when I had started. I now had to take a step back and rethink my game plan because now the shop and I were both married to this vehicle and we had to come up with a resolution. This was a case of automotive polygamy and this truck was not letting go of either one of us.

Figure 10: P/S Pressure Switch unplugged

I knew from prior experience that the five-volt reference line can leave a PCM and feed multiple sensors, and if any one of those sensors shorted the line internally to its ref ground, or the line itself shorted to ground, then all the sensors associated with that line would suffer. I had isolated the independent accelerator sensor five-volt circuit from the PCM properly, the five-volt regulator feeding sensor #2 had a five-volt reference feed that seemed to be okay, and there were other independent five-volt ref feeds. Then I thought, “What if these independent feeds had a common regulator within the PCM and one of the five-volt ref feeds outside the PCM was shorted and back-feeding into the PCM?” I now had to view the entire PCM diagram and determine how many five-volt feeds were leaving the PCM and how many of those five-volt feeds were externally shorted. Then I could build a new diagram to show how the PCM feeds these sensors from a common five-volt regulator.

Figure 11: A/C Pressure Switch unplugged

By testing the harness at the PCM, I discovered that accelerator sensor #2 and the TPS #1 and #2 reference voltage feeds were okay. The EVAP sensor, A/C pressure sensor, P/S pressure sensor, and accelerator sensor #1 circuits were all shorted with no five-volt reference feed. I now drew a new diagram to reflect my findings (Figure 9) so that it would help me better understand where I went wrong. I next decided to do an isolation procedure by unplugging all four sensors one at a time. If the short did not go away, I was dealing with a shorted circuit to ground leading to any one of these sensors. I first unplugged the accelerator sensor with no results, then I unplugged the P/S pressure sensor (Figure 10) and the short was still there. I next unplugged the A/C pressure sensor — no change (Figure 11).

I now needed to get the vehicle up on the lift to access the EVAP sensor. As I was trying to locate the EVAP sensor in the right rear of the vehicle, I was suddenly taken aback by what I saw. The tail pipe had broken and the customer must have ripped it off the truck. This allowed hot exhaust gases to directly contact the main wiring harness that runs along the right side frame rail (Figure 12), melting it in such a fashion that the EVAP pressure sensor five-volt reference line was shorting to a ground wire.

Figure 12: Melted ECM harness at R/R suspension from broken tailpipe

What a turn of events and a final end to my short-lived marriage to this vehicle! It was something I never expected to see, or even thought could happen. This was real curve ball that gave me a run for my money. I just never knew that independently-fed five-volt reference lines could be joined within a PCM. I had thought there would be a five-volt regulator for each sensor. In the past, I have seen five-volt lines feed out of one terminal of a PCM and branching off to four sensors, so you knew they all shared the same five-volt regulator. This one was a learning experience for me, and I hope for you as well.

Vintage Story: 2002

I was called to a shop for a no start on a 1997 Isuzu Rodeo with a 3.2L engine. The shop had just replaced the engine with a rebuilt unit from an engine rebuilder because it had some internal mechanical noise issues and now after the installation was done the vehicle had no spark or fuel pulse. The shop checked the wiring harness connections on the engine and made sure all grounds were properly secured but could not come up with a solution. It was a simple R&R operation that the head mechanic performed and he was very careful to put everything back in its proper place as he transferred components from one engine to the other on the shop floor. This is the type of situation we have all been in at one time or another and it is not a pleasant one. Especially if you have a customer breathing down your back and calling every day to see what progress was being made. The shop was pressed for time so they decided to call me in for technical support.

Figure 1: The SIMU-TECH in sweep mode to do a full harness check of all powers and grounds to make sure the ECM had what it needed.

When I arrived at the shop I first did a visual inspection within the engine compartment and everything seemed to be in order. I placed my scanner on the vehicle to see if the ECM was functioning. I did have communication and all the data was within specification but the ECM failed to trigger the independent coils and injectors when I cranked the engine. I placed my SIMU-TECH unit on the vehicle to prove out the harness. This machine had the ability to interface with the ECM harness by use of a computerized breakout box and a custom made interface cable that plugged in between the ECM and its connectors. I wanted to do a full harness check of all powers and grounds to make sure the ECM had what it needed so I placed the SIMU-TECH in sweep mode (Figure #1). All the power feeds, ground feeds and sensor values were all checked and validated for proper specification. All relays, solenoids and injectors were also checked for proper resistance, voltage supply and amperage draw. This was all done within a matter of minutes. The SIMU-TECH was designed to do a full harness check so knowing that the ECM harness passed the integrity check it was now time to use the SIMU-TECH seven-trace scope to prove out some dynamic signals responsible for engine start up.

Figure 2: I cranked the engine and the signals seemed to be correct, but I wasn’t too sure if the signals were in proper alignment with one another.

I knew the ECM needed the proper RPM signals before it could perform a task so my next move was to monitor the crank and cams signals to make sure they were toggling at the proper thresholds and frequency. I also needed to see if the crank and cam signals were in proper synch with one another. I placed the SIMU-TECH in waveform viewer and selected the crank and cam signals. I cranked the engine and the signals seemed to be correct (Figure #2) but I wasn’t too sure if the signals were in proper alignment with one another. I did not have a good known waveform for this vehicle to compare notes on so I had to go with what I knew. I could see from the waveform that both the crank and cam signals were properly toggling from 5 volts to ground. The cam signal did provide a full square wave pattern from high to low transition and at the same time the crank sensor provided two groups of a double synch signal followed by 5 pulses (this indicating 2 crankshaft rotations). The signals looked good but I could not be sure if the signals were properly in synch with one another. At this point I told the garage mechanic to pull the timing cover so that we could inspect the timing belt and gear-to-shaft orientation for flaws. Maybe there was something that was out of alignment.

Figure 3: I returned to the shop the next day to inspect the timing belt

I returned to the shop the next day to inspect the timing belt (Figure #3). I was surprised to find everything was in order. The marks all lined up properly and there did not seem to be any shaft to gear damage. It is not uncommon to have a timing belt on the money and have a timing gear move on a shaft do to a sheared key or locating pin. I was now running out of ideas for this nightmare Isuzu. It seemed like I was hitting a dead end in all directions. I left the shop to hopefully regroup my thoughts to come up with a new game plan for my third visit. I finished the day out diagnosing other cars with success but I still had this Isuzu in the back of my mind. I decided to go home and do some digging for information to help myself build my next plan of attack. I had lost a battle but not the war……..

Figure 4: When I got there I could see the mechanic was very sad and he handed me a stick man drawing he made

The next day I woke up with another plan. This was a rebuilt engine and what if the crankshaft was not machined to the specs of the old one. I had an idea! I called the shop and told them to pull the crankshaft sensor and turn the crankshaft so the double notch on the crank pulse ring lined up with the hole. Then I told them to mark where the position of the crankshaft keyway was in relation to the engine block markings. Next I told them to do the same with the old engine just to see if the pulse rings were synched properly on their shafts. As far-fetched as this seemed it was all I had to offer.

Figure 5: The mechanic pulled the oil pans on both engines and by looking at the old crankshaft pulse ring...

The shop later called me back and told me they found the problem. They would not tell me over the phone but only said to bring my camera. When I got there I could see the mechanic was very sad and he handed me a stick man drawing he made (Figure #4). This drawing as funny as it was prepared me for what I was about to see. The mechanic pulled the oil pans on both engines and by looking at the old crankshaft pulse ring (Figure #5) you could see the major difference with the pulse ring in the rebuilt engine (Figure #6). The rebuilder had given the shop a 93′-95′ Isuzu 3.2L engine instead of 96′- 98′ application. The difference was only in the crankshaft trigger wheel design where Isuzu changed the strategy of the RPM signals. What a mechanic’s nightmare! This brings to life the true meaning of getting the shaft. A lesson to be learned of how we need to be more cautious and alert to the parts we purchase.

Figure 6: ...you could see the major difference with the pulse ring in the rebuilt engine

Figure 7: I hooked up my SIMU-TECH once more to get a good waveform of the crank/cam signals for my library collection

About a week later I returned to the shop after they installed another engine at the cost of the rebuilder. I hooked up my SIMU-TECH once more to get a good waveform of the crank/cam signals for my library collection (figure #7). As you can see from the waveform the crank signal has multiple pulses followed by one large synch pulse. Unlike the pattern on the rebuilt engine where there were only 5 single pulses followed by a double pulse. This is what the ECM was looking for.

Vintage Story: 2001

I was called to a shop for a complaint on a 1995 Olds Ciera with a 3.1 “M” engine that had a CEL lamp on with a stored code P1405 (EGR 3 Solenoid Error). The shop had put the Scanner on the vehicle and found the EGR code as a history fault. They did a visual inspection of the EGR solenoid harness to make sure the harness was not damaged. They also checked for proper power supply to the solenoids as well as checking the solenoid circuits leading back to the ECM. With everything checking out electrically they decided to replace the EGR valve assembly. When the problem still occurred the shop decided to call me in for a second opinion. They did not want to try replacing the ECM because this would have been a very expensive guess.

This EGR system consisted of an EGR valve with three internal solenoids (small, medium and large orifice). The ECM would energize the appropriate solenoid depending on the amount of EGR the engine needed. The solenoid assembly is feed ignition feed and each solenoid in turn was controlled by a driver within the ECM. The ECM never set a driver code so this was a good indication that there were no open or short circuits within the system. But there still seemed to be an issue relating to the #3 solenoid within the EGR solenoid assembly or the solenoid driver operation within the ECM.

Figure 1: Data stream information.

I started my diagnostics by viewing the data stream information (figure #1).The ECM set a code P1405 to indicate that the EGR #3 solenoid was not performing its task. This did not mean that the solenoid was necessarily bad but that there was a problem with the operating system of the EGR. It is important to understand the operating and failure strategies of an ECM. The ECM will ground the solenoid and monitor the circuit electrically to see if the solenoid circuit was indeed high and went low when commanded and that the proper current levels of the solenoid are within range. This is done by the Quad driver circuit in the ECM. After the EGR solenoid is grounded the ECM will monitor the O2 response and look at the Block Lean/Integrator values to see if the system went lean. If there was no reaction it may wait until the largest orifice is opened. If there still is no response then it will illuminate the CEL lamp.

Figure 2: Scan tool in graphing mode, monitoring the EGR command signals while power braking the engine in drive.

I placed my scan tool in graphing mode (figure #2) and monitored the EGR command signals as I power braked the engine in drive. The ECM was commanding the EGR solenoid drivers as I held the engine at part throttle. This may not always be a valid check procedure because this only shows you what the ECM is in the process of doing but does not prove whether the internal drivers are actually grounding the solenoids. The only way to really determine if work was being done would be to hook up a scope to visually see the ECM ground each solenoid driver. Viewing a command signal does not always guarantee a circuit activation especially if there is a bad driver within the ECM.

Figure 3: A sweep test of the ECM harness to prove out the integrity of the wiring

I placed my SIMU-TECH computerized breakout box on the vehicle and interfaced it between the ECM and its harness. I quickly did a sweep test of the ECM harness to prove out the integrity of the wiring (figure #3). The EGR solenoids all had the proper supply voltage of about 11.84 volts flowing through each solenoid all the way back to the ECM terminal pins. The SIMU-TECH did ground each driver circuit and recorded about 430 mA of current draw on solenoids #1 and #2 and about 1147 mA of current draw at solenoid #3. The largest orifice was controlled by the #3 solenoid and it required a larger solenoid so it was normal for the current draw to be twice the current draw of solenoids #1 & #2. This test procedure did rule out any open or short circuits from the EGR solenoids to the ECM but now I had to see what the ECM was actually doing by using a scope.

Figure 4: SIMU-TECH in scope mode to monitor EGR solenoids and TPS sensor.

I used my SIMU-TECH in scope mode and selected 3 traces to monitor all three EGR solenoids and a 4th trace to monitor the TPS sensor to monitor the position of the throttle plates at part throttle load (figure #4). You can see the ECM grounding both the #1 & #2 solenoids at the same time and then apply the #3 solenoid at a longer on time. This proved that the ECM was functioning properly and doing its job. The internal drivers were working and the ECM was not the culprit at hand. Okay so now we knew the ECM desired to apply the solenoids, the harness was intact and the solenoid drivers were doing their job but why the solenoid #3 error?

Figure 5: The passage running from the EGR valve to the throttle body was plugged solid with carbon

I now decided to go directly to the EGR valve to activate the solenoids manually to make sure they indeed were moving. Just because a circuit is energized does not guarantee movement. A binding solenoid or other mechanical problem with the valve could prevent application of the valve to open. As I activated the solenoids I could hear the valve apply but there was no change in the way the engine ran. The EGR passage had to be clogged. With 73,000 miles on the clock this vehicle was a good candidate for an EGR restricted passage. I instructed the garage to remove the EGR valve and the throttle body to get a close view of the EGR passage. What a surprise! The passage running from the EGR valve to the throttle body was plugged solid with carbon (figure #5). This EGR passage needed a severe angioplasty procedure to bring it back to specs…………

During a diagnostic procedure it is always important to build a game plan for yourself. You need to understand system operation so you know how the entire circuit functions. You must also understand failure strategy of a component so you know what the ECM expects to see. Then you can attack the system from different areas of concern and hopefully find the culprit without too much wasted time and parts.

Figure 1: 2003 Pontiac Bonneville SSEI with no power window operation.

I was called in to a shop for a complaint of no power window operation on a 2003 Pontiac Bonneville SSEI (Figure 1). They had already checked the power and ground feeds at the driver door master switch and everything seemed okay. The odd thing was that the other door windows would not operate from their individual switches. It was just hard to believe that this vehicle could have four bad window switches. The window motors all worked okay when power and ground were applied to each motor individually. The garage was uncertain where to turn, so rather than throwing parts at this car they decided to call me in for a second opinion.

When I arrived at the shop I verified the complaint by trying each power window switch and nothing responded. I next decided to print out a wiring diagram to familiarize myself with the system layout and see if I could find something in common that would affect power window operation at all four doors, such as a main power or ground feed. As I viewed the diagram, I found out that these were not your everyday “how you doin’” window switches. Instead, they were all separate door control modules. Each module in turn controlled window motor operation through an internal window motor driver. Operating the window switch only created a high/low signal to command the window up or down. The switch no longer had to transmit a power or ground feed to the window motor directly, which made for less wear and tear on the switch contacts.

Figure 2: Color-coded Power Window Circuit diagram. Green: Grounds, Purple: high-current circuit breaker feed, Orange and Red: low-current battery feed.

I used my Paintbrush function in Mitchell to color-code the wiring diagram. I chose green for the grounds, purple for the high-current circuit breaker feed, orange and red for low-current battery feed (Figure 2). The ground feeds for each door module were at different locations, so it was hard to believe that the system had four open grounds. The rear door modules shared the same low-current battery feeds, but the front door modules had two other separate low-current battery feeds, so here too nothing seemed common to all four door modules. Looking a little closer at the diagram, I could see that all four modules did share the same high-current feed from a 30 Amp circuit breaker, so this was the first place I wanted to look.

Figure 3: I discovered that the driver door module had the ability to communicate with a scan tool by looking at a data communication wiring diagram, which showed all the onboard controllers on the serial data network linked to the ALDL connector.

Figure 4: Looking at the scan tool, I pulled some "U" codes of interest

Figure 5 : After I had the shop remove the front driver's seat, and as I lifted the rug I noticed a lot of rust build-up on the floor from a prior water leak

Figure 6: A conduit that held the splice internally wrapped with black electrical tape

According to the diagram, there was a splice for this private UART network located under the rug about 14cm from the left power seat breakout. I had the shop remove the front driver’s seat, and as I lifted the rug I noticed a lot of rust build-up on the floor from a prior water leak (Figure 5). I next located a conduit that held the splice internally wrapped with black electrical tape (Figure 6). I slowly removed the tape and was surprised to see a Scotch Lock connector joining all four UART lines going to the door modules (Figure 7). This connector was badly corroded and was barely making a connection for all the wires to share. I removed all of the wires and repaired the splice. Suddenly, all the windows were working fine.

Figure 7: I removed the tape and was surprised to see a Scotch Lock connector joining all four UART lines going to the door modules.

So, now the recap on this whole scenario. I discovered that the door modules were on a private network with each other and even though they had their own power and ground feeds and switch signals, they all refused to operate when they were unable to communicate with one another. It was a default built into the system. What was amazing to me was why any manufacturer would use a Scotch Lock to connect these wires inside a harness running along a floorboard. Wouldn’t it have been better to use a solder joint located in a higher area not so susceptible to water damage? But, then again, who am I to second-guess the engineers? There’s always the possibility that this was a field repair done by another shop.

I hope this story has enlightened you to better understand how a network, whether large or small, needs to be in proper order, or things may not work the way they were intended to. Just doing a simple power or ground check at a component does not always validate system integrity. Parts replacers beware!

2005 Jeep Wrangler with a 4.0L engine experiencing a no start condition.

1. You may come across a 2005 Jeep Wrangler with a 4.0L engine experiencing a no start condition. Check the ASD relay feed circuit for a blown fuse.

This fuse will blow when the ignition coil noise suppressor wiring comes in contact with the oil dipstick tube and rubs through the insulation.

1998 Nissan Altima with a 2.4L with no spark after a recent engine replacement.

2. You may come across a 1998 Nissan Altima with a 2.4L with no spark after a recent engine replacement. Take a close look at the Ignition coil and cranksensor connectors to see if they are not crossed. They are identical connectors and they are right near each other making it easy to mix them up.

Figure 1: 2007 Jeep Grand Cherokee

I was called in to a shop for a complaint of erratic engine operation on a 2007 Jeep Grand Cherokee with a 5.7L engine (Figure #1). The engine would run fine with no problems for a while, but at any given moment it would begin to abruptly surge up and down and cut out. The engine could be immediately restarted and would run perfectly again until the next episode. The shop had installed high-performance spark plugs and ignition coils a few weeks earlier, but there were no drivability complaints at the time. The shop even put the old ignition coils back into the engine, but the problem still remained. There were no codes stored in the PCM memory, and the shop did not want to start playing Russian roulette with auto parts, so they called me in for tech assistance.

Figure 2: EScan shows no codes in memory

When I arrived, I attached my Escan generic OBD II scan tool to the vehicle to check for codes — none were recorded in memory (Figure #2). I started the vehicle and it seemed to run okay, but then it suddenly started to run erratically with a bouncing tachometer. The engine seemed to dip in and out with a near-stall condition. After a few seconds of this, the engine just cut out as if the ignition key had been turned off. I immediately restarted the engine and the problem was gone. I ran it again for quite a while and could not reproduce the problem. It was as if the crank or cam sensor was giving an erratic signal, or the PCM had an internal board issue. I could no longer reproduce the problem, so I offered the garage a free opinion: Try a new crank sensor due to their high failure rate. It would be a cheap fix if it worked.

The shop called back the next day and told me that the crank sensor did not fix the problem and that they had rechecked all the PCM power and ground feeds. The shop was willing to try a new PCM since the problem was so intermittent and everything seemed to lead to an erratic computer. I agreed to program the new PCM for them in hopes that the problem would go away. I could not think of anything else that could cause such an erratic problem. I went there the next day after the new PCM was delivered to program it with new software and configure it to match the vehicle. I started the Jeep and it ran fine for the first 15 minutes, but then it went back into its dance. At this point I got that feeling we all get when we realize that there is an expensive unneeded part installed that someone has to take the blame for. At this point, the shop I were both now married to the vehicle, and we had to find the problem or this PCM was going to be this evening’s meal.

Figure 3: Graphing data parameters

I knew my timeframe was short for finding the culprit because I had no idea how long the problem was going to stick around. I quickly placed my Escan tool on the vehicle and graphed some PCM parameters to see if anything looked unusual or out of range (Figure #3). I was monitoring the rpm, MAP and TPS sensors and could see the engine rpm going into an idle roll. But then something unusual happened — I lost communication with the PCM as the problem got worse (Figure #4), then the engine cut out. This had to be a loss of power or ground to the PCM, or possibly a reference voltage feed momentarily shorting to ground because the PCM was shutting down operations at the same time as it decided to no longer communicate with my scan tool. The only way I was going to nail this problem would be with a multi-trace scope to watch as many signals as I could before this problem decided to go away.

figure 4: Loss of scanner communication

Figure 5: ECM releasing ASD relay coil

Figure 6: Checking for loss of cam signal

I used my eight-trace Escope and quickly selected six main items that would help me pinpoint the problem using my different colored leads as follows: white for PCM battery feed, blue for PCM ignition feed, red for PCM Auto Shutdown Down relay feed, purple for ASD relay coil driver, yellow for 5V reference, and green for PCM ground. As the engine started to run erratically, I captured my first event (Figure #5). I could see that the ASD relay driver momentarily was released by the PCM under 50ms, but I never lost my 5V reference, or my powers and grounds. It was as if something was telling the PCM to let go of the ASD relay coil, so I now had to dig a little deeper. I wanted to see if I was losing a cam or crank signal, so I captured two more events using my green lead for the cam signal (Figure #6) and my yellow lead for the crank signal (Figure #7). Neither waveform pattern showed a loss of cam or crank signal when the ASD relay was being released, but the tachometer was definitely following the cutting in and out of the engine.

Figure 7: Checking for loss of crank signal

Figure 8: Scoping all 8 coil drivers

I had an eight-trace scope, so it was to my advantage to monitor all eight ignition coil primary circuits to see if any coil trigger was dropping out. I moved all my leads to the coil drivers and continued to monitor the engine’s operation. Today was my lucky day because this problem was only getting worse and it decided to stick around and give me a joy ride. When I captured another event (Figure #8), I was surprised to see that I was losing all eight coil drivers at the same time. The PCM was letting go of the ASD relay coil and it did not start to trigger the ignition coils again until about 300ms later. There was something making this PCM halt all operations momentarily, or I possibly had a bad new PCM on hand. It would not be the first time I have come across a defective new part.

I decided to call Bernie Thompson from Automotive Test Solutions just get his opinion on things because everything I have done so far has lead me to erratic PCM operation and I just could not pinpoint the cause. I could see what the PCM was doing, but what was its reasoning? Bernie basically wanted me to go back to my scope and look below the zero line for any secondary voltage kickback that could cause a PCM-reset condition. That’s when outside noises penetrate the PCM through electromagnetic interference and disrupt its normal algorithms, making it momentarily skip a beat. The engine in no way or fashion had an engine misfire due to a bad ignition coil or spark plug, but it still seemed like a logical possibility.

Figure 9: Secondary KV spikes present

I went back to my primary pattern and this time lifted it off the zero line to expose any activity below (Figure #9), and I was surprised to see multiple cylinders getting hit with secondary kickback voltage. Cars using PCMs that directly control coil primary may have a little secondary kick that may not have any effect on PCM operation, but if the kick does get great enough it could give the PCM a momentary heart attack and make it skip a beat, or, worse, do permanent damage to the PCM or an internal coil driver.

Figure 10: Comparing performance spark plug

I knew the original coils were put back in, but I was not so sure about the spark plugs. I had the shop pull a spark plug to get a look at what was currently installed in the engine. I then compared that spark plug to the original (Figure #10), and there was something funky about it. It had a triangle-shaped electrode for a special performance feature it offered. I had the shop remove all the spark plugs and put factory spec spark plugs back in. Once this was done, the problem was completely resolved.

I can only tell you that I was taken aback by this turn of events. It is just so hard to believe that a company could manufacture a spark plug for performance purposes without any regard to its effects in a coil-over-plug environment. The problem it created mimicked a failed PCM that any tech would have automatically changed in the field. There were no codes, no sensor failures, or wiring issues. A multi-trace scope would have to be used to find a cascading effect of events that would point you in the right direction. I own many one-, two- and four-trace scopes, but with so many circuits involved with onboard control modules today, it sometimes makes more sense to use a bigger net to throw at a problem rather than fishing around with only a few hooks.

Figure 1: 2008 Nissan Altima with a 2.5L engine with no A/C compressor engagement.

I was called to a shop with a complaint of no A/C compressor engagement on a 2008 Nissan Altima with a 2.5L engine (Figure 1). The vehicle was recently involved in a front-end collision and the PCM and engine harness were both replaced. The technician had checked all fuses and rechecked the harness connections, but could not resolve his diagnostic dilemma. The inside A/C panel responded to selections and the LED on the panel illuminated when the A/C mode was selected. The system was properly charged with and there were no service codes present in the PCM when a scan tool was connected. At this point, the shop decided to call me in for a second opinion.

Topology Network View

Figure 2: Nissan Consult III readings

When I arrived, I hooked up my Nissan Consult III to the vehicle to confirm the shop’s findings. I selected the topology network view (Figure 2) to see all the controllers on the network at the same time and to see if there were any codes stored in any of the operating systems. Network view is a feature that many factory scan tools are beginning to support. Not all manufactures are doing it, but the industry is slowly moving in this direction. It provides a technician with a quick visual mapping of the entire vehicle by the use of colored icons representing each control module. These modules will be different colors depending on if they have current, history, or no codes stored in memory. The lines drawn among the controllers may also use color coding to represent different types of networks, or even networks that no longer respond. This type of layout allows the technician to build quick associations with controllers when problems arise within the network. By simply looking at the network, I could see that there were no trouble codes within the PCM or any of the other controllers. The Audio Video controller was not responding on the network because it was an option that was not present, as the red line drawn to it indicates.

Figure 3: A/C system diagram printout

I did not know the system strategies of how the A/C compressor was controlled on this vehicle once the A/C button was pressed. The command was sent out into the network, but the request path was something I needed to find out. I first printed a diagram of the A/C system (Figure 3) and I was surprised to see that the Integrated Power Distribution Module (IPDM) was in charge of controlling A/C relay operation, but it was not grounding the relay when the A/C-on command was sent from the A/C panel. I used the scan tool to navigate to IPDM data (Figure 4) and could see that the IPDM was not receiving a request to activate the A/C relay. This request was being suspended somewhere in the network between the A/C panel and the IPDM, but the question was where. It was a request that had to travel through the CAN network, which the IPDM was tied to. I just had to dig a little deeper to find out which controller or controllers were responsible for giving the final command.

Figure 4: Data Monitor - IPDM E/R

BCM & IPDM

Figure 5: A/C control panel diagram printout

I next printed out a diagram of the A/C control panel to see where the command signal was being sent (Figure 5). By looking at the diagram, I could see that the request was sent directly to the Body Control Module by a command signal line from the A/C control panel. I used the Consult III to navigate to BCM data (Figure 6) so I could validate that the BCM did indeed see the request from the A/C panel. The BCM definitely was receiving the A/C-on command, but there had to be another controller that had higher authority in controlling the A/C command output because the BCM did not pass this command on to the IPDM controller. The only computer on the CAN network that would have more authority over the BCM for the A/C command would have to be the PCM. Engine control modules have always been in control of A/C relays in the past because they had to look at more criteria than most controllers on the network prior to making a final decision on A/C clutch activation.

Figure 6: Data Monitor - BCM

Color Confusion

Figure 7: Powertrain Control Module diagram printout

Engine controllers will usually take into consideration data PIDs such as coolant temp, throttle position, power steering pressure, or possible A/C input sensing devices. I had to print out a diagram of the Powertrain Control Module to see how it played a role in the activation of the A/C clutch (Figure 7). By closely looking at the diagram, I could see that the A/C pressure sensor was directly tied to the PCM to monitor the operating range of the pressure within the A/C system, so I decided to use the Consult III to navigate to the PCM data stream and pull up some PIDs of interest (Figure 8). It is important to fully understand the operating ranges of sensors because there may be situations where a sensor value is still within range, yet causes a system-related problem without ever setting a code. The sensor values I selected were rpm, Coolant Sensor, Throttle Position Sensor 1, Throttle Position Sensor 2, A/C Signal out, Power Steering Switch signal, A/C Relay Command, and A/C Pressure Sensor. After viewing the data, I noticed that the A/C pressure was at 0 volts indicating low refrigerant pressure in the system. The PCM never set a code, but decided to keep the A/C clutch off due to the low-pressure condition. The system was properly charged, so there had to be an issue with the A/C pressure sensor or its wiring.

Figure 8: Data Monitor Engine

Figure 9: Testing the A/C pressure sensor for proper ref voltage and ground feed

I located the A/C pressure sensor at the left front of the engine compartment (Figure 9) and tested the wires for proper ref voltage and ground feed. Keep in mind that a low signal output is always an indication of a shorted or open signal line to the PCM, or an open or shorted ref voltage line to the A/C pressure sensor. What I discovered was that there was no reference voltage on the pink wire at the A/C pressure switch, and the circuit was not shorted. I now had to find my way back to the Integrated Power Distribution Module to check the circuits going in and out of it. The information system I was using could not provide me with a connector view of the IPDM, so I had to resort to another information system (Figure 10). Looking at the connector view, I now knew where the pins were located in the IPDM, but I also had conflicting information with the diagram colors from the first information system I had been using. Checking the Pink 5 volt ref at pin #103 showed no ref voltage, but the 5 volt ref into the IPDM from the PCM was not Brown and White at pin location #24, but rather Green (Figure 11).

Figure 10: IPDM connector view

Figure 11: 5 volt ref into the IPDM from the PCM was Green

Figure 12: Checking the Green ref voltage line

The wiring diagram information was correct on pin location, but wrong on color identification. This is something that can happen with any information system, so you need to be very alert and even have another information system available to compare notes with. If you look closely at the wiring at the upper right side of the IPDM, you can see that the Red and White wires were twisted together to use the White ref ground wire to cancel any noise on the Red signal line. On the left center of the IPDM, the Gray and Blue wires were twisted together using the Blue ref ground to cancel noise on the Gray signal line. When I checked the Green ref voltage line (Figure 12), I discovered that the PCM was sending the 5 volt ref to the IPDM, but the ref voltage was not coming out of the IPDM on the pink wire. The IPDM had an internal board problem. I then went one step further and started to flex the module. I heard the A/C clutch engage! So, I monitored the PCM data and flexed the IPDM again, and I captured a screen shot (Figure 13). You can see that the pressure switch was reading the proper output of about 1.3 volts.

Figure 13: Data Monitor Engine

When this car was involved in the collision, the IPDM most likely got damaged from the impact. There was no visible damage to the unit, but the shock was enough to create an internal open circuit in the A/C pressure sensor circuit. There were no codes in the network to point me to any areas of concern. The only thing that allowed me to find the problem was knowing how the system worked and how to read scan data. It is also important for the technician to be aware that his information is not correct, which will keep him from going down the wrong path.

2002 Chevy Monte Carlo with a 3.8L engine experiencing a loss of power

1. You may come across a 2002 Chevy Monte Carlo with a 3.8L engine experiencing a loss of power, engine stall or erratic idle surge. Take a close look at the intake plenum where it meets the throttle body. The plastic intake will get a hole melted through it where the hot EGR gases pass through it. This is usually caused by a clogged catalyst convertor when it creates a higher than normal exhaust back pressure pushing hot exhaust gases back up into the EGR passage way.

2003 Audi A4 with a no start condition.

2. You may come across a 2003 Audi A4 with a no start condition. Remove the ECM in the upper left hand firewall and you will find a relay center below it. This area is prone to water intrusion when the windshield drains are clogged damaging the EFI relay.

2002 Mazda Protege with a 2.0L with a rough idle and low engine vacuum.

1. You may come across a 2002 Mazda Protege with a 2.0L with a rough idle and low engine vacuum. The engine may run fine above part throttle and set no codes. This could be caused by a partially stuck open EGR valve. To quickly check for this don’t spend to much time unbolting the EGR valve at the firewall side of the engine. Simply remove the EGR exhaust feed pipe at the front exhaust manifold and block it off.

1998 Chevy G3500 Van with a 5.7L engine experiencing a rich condition with multiple injector driver codes.

2. You may come across a 1998 Chevy G3500 Van with a 5.7L engine experiencing a rich condition with multiple injector driver codes. Take a close look at the engine harness where it comes in contact with the transmission dipstick tube. The wire harness will rub through and short the injector driver circuits to ground.

Figure 1: 2006 Lincoln Navigator with a 5.4L and a rough-running engine complaint

I was called to a shop on a 2006 Lincoln Navigator (Figure #1) 5.4L with a complaint of a rough-running engine. The techs pulled some O2 sensor lean and rich codes along with some variable valve timing codes. They were not too familiar with the operation of the variable valve timing system on this vehicle, so they decided to get a more in-depth diagnosis before making any major decisions on where to go.

When it comes to variable valve timing systems, there are indeed a lot of variables involved. The basic strategy of the PCM is to determine how much duty cycle it will provide to each cam actuator solenoid to allow oil pressure to pass through the cam actuator thus moving the camshaft gear on the end of the camshaft to accommodate an advance or retard position relative to that of the crank. A lot can go wrong, such as a sticking solenoid or actuator, or even clogged oil passages. Blame poor oil maintenance, or wear and tear from high mileage. There are also electrical failures such as open or shorted actuator solenoid circuits, or a possible failure of the solenoid driver within the PCM.

Figure 2: A Generic Escan tool to pull and verify the codes that had already been retrieved

When I arrived at the shop I hooked up my generic Escan tool just to pull and verify the codes that had already been retrieved (Figure #2). There were P0011 and P0022, which related to the position of Bank #1′s camshaft being over-advanced, and Bank #2′s camshaft being over-retarded. The PCM in this vehicle was using two camshaft positioning sensors to perform a check and balance of the variable valve timing system. The command was given to each camshaft to move to a certain position while the PCM had the ability to validate if the camshaft sprockets were actually in the correct commanded positions. There were also O2 codes P2195 and P2198 stored in memory stating that Bank #1 was running lean while Bank #2 was running rich. These O2 codes were in the mi,x but you need to keep in mind that an engine with mechanical or hydraulic problems can easily mess up the fuel trims and create a lean or rich condition. So, I decided to home in on VVT.

Figure 3: Power braked the engine to wide open throttle and graphed my readings within the program

I knew that a valve timing issue would easily show up in a volumetric efficiency test without my getting too intrusive. I already had the Escan tool hooked up, so it was just a matter of plugging in some criteria information to test the volumetric efficiency. I set the engine size to 5.4L, ambient air temp to 86 deg. F., and my elevation at sea level. I next power braked the engine to wide open throttle and graphed my readings within the program (Figure #3). The red graph represents the theoretical air flow as calculated by the program, while the yellow graph represents the actual volumetric flow. By looking at the yellow graph you can see that not only was the volumetric efficiency of this engine low, but the air volume was moving in and out of the MAF sensor. I have seen this erratic air flow many times before using this VE graph and it is usually a clear indication that the engine either has a clogged exhaust or a valve timing problem where the intake valves are not properly closing as the piston is reaching top dead center of the compression stroke.

Figure 4: 1st step: verify which cylinders were creating the roughness in the engine.

To stay in the driver’s seat of diagnostics and still not being too intrusive, I decided to hook up my Ford IDS scan tool for some enhanced engine diagnostics that the tool claimed to perform. My first step was to verify which cylinders were creating the roughness in the engine. This I did by using the power-balance mode (Figure #4). In this mode I was able to see the PCM monitor the speed of each individual cylinder’s crank throw by means of the crank sensor. You can see that cylinders #5, 6, 7 and 8 were all below the zero line. Normally this pattern would run close to the zero line with slight deviations of plus or minus 5% and any large “V” spike below the zero line would indicate a misfire. Taking into consideration that cylinders #5, 6, 7 and 8 all share the same Bank #2 cylinder head, I was leaning toward a valve train problem with that bank.

Figure 5: A cranking compression chart captured when cranking the engine at wide open throttle.

I moved on to the cranking compression test that I have found to be a solid Ford IDS procedure that has yet to let me down. Again, this uses the crank sensor to determine the speed of each cylinder as it monitors the slow-down of crankshaft speed as each piston comes up on the compression stoke. A weak cylinder doesn’t slow the crankshaft as much as much as a stronger one does, thus showing up as a low-compression cylinder. As I cranked the engine at wide open throttle to prevent the injectors from firing, I captured a cranking compression chart (Figure #5). You can see by the chart that cylinders #5, 6, 7 and 8 all had low compression as compared to Bank #1′s cylinders. It’s convenient that this can be done without ever having to pull the spark plugs and measure the compression of each cylinder with a mechanical gauge. This is technology at its best!

Figure 6: The camshaft timing parameters for each bank on the scan tool

The validation process was all pointing toward a possible jumped timing chain on Bank #2. It was just unlikely that one head would have four bad cylinders with leaky valves. The common cause of low compression in four cylinders in the same head would most probably be a valve timing issue. I now wanted to do one more check to find out what the PCM was seeing when it set the variable valve timing codes, so I decided to look at the camshaft timing parameters for each bank on the scan tool (Figure #6). By looking at the data with the engine idling in its rough mode, I could plainly see VCTADV for Bank #1 was at 0 degrees at idle, but the VCTADV for Bank #2 was close to 60%, indicating that the cam sprocket on Bank #2 was out of correlation to the crankshaft. At this point I had gathered enough information to validate the removal of the front timing cover.

Figure 7: The tech had pulled the timing cover and lined up the crank so the keyway was up at the 12 o’clock position.

Figure 8: Whiteout on both cam sprocket marks and I could see the driver cam sprocket timing mark was properly lined up with the center of the camshaft hold-down cap.

I went back to the shop the next day and the tech had pulled the timing cover and lined up the crank so the keyway was up at the 12 o’clock position (Figure #7). I placed whiteout on both cam sprocket marks and I could see the driver cam sprocket timing mark was properly lined up with the center of the camshaft hold-down cap (Figure #8). When looking at the Bank #2 cam sprocket (Figure #9), I could easily see that it was off by a few teeth. The timing chain had jumped, which caused the engine to run very poorly and the PCM to set timing position error faults. I felt good about my findings because I did not want the shop to go through all the work of ripping down the front of the engine just because it “felt” like a timing chain issue. I had to be sure on this one.

Figure 9: Bank #2 Sprocket

It was a very interesting turn of events to be able to literally sit in the driver seat and do performance tests and mechanical diagnosis using only scan tools. I sat comfortably inside the vehicle and didn’t even have to open the hood or get my hands dirty. I must say that as these engines and operating systems get more advanced our diagnostic jobs get physically easier, if more intellectually challenging. You just can’t be too quick to jump the gun. Rather, set up a series of test procedures for yourself to better home in on the problem. This will lead to a successful diagnosis with very little time wasted.

2001 VW Jetta with a bucking problem on acceleration

1. You may come across a 2001 VW Jetta with a 2.5L engine that may experience a bucking problem on acceleration. There may be no codes stored in the system. Remove the air cleaner housing and inspect the main body ground. It is common for the negative battery cable to break away from the body and rest against the stud causing a make and break connection.

1998 Chevy G3500 with a high or low idle, and a code P0507 stored in memory

2. You may come across a 2005 Chevy G3500 with a 6.0L engine experiencing a high or low idle with a code P0507 stored in memory. Do not be too quick to replace the throttle body. These vehicles have a common problem where the IAC control valve wiring will break clean right at the connector and will be held only in place by the wire insolation. When inspecting the connector give each wire a slight pull to feel the soft spot. The wire will then break away like it did here.

Figure 1

I was called to a shop to perform a program update on a 2006 Ford E250 van with a 6.0L engine (Figure 1). This is a task I am asked to do on a daily basis. There are many shops that do not make the investment to purchase a programming interface, or to subscribe to automotive manufacturer websites to download programming files. This may be due to the fact that they may not get enough calls for reprogramming to justify the cost, or they may not want to expose themselves to the liabilities involved in reprogramming.

Figure 2

There are many precautions that must be observed while programming a vehicle. The most important one is having the proper battery charger, such as the Fronius Power Supply (Figure 2). This device will maintain a uniform voltage in the battery under the different load conditions caused by power consumption changes during reprogramming, as when cooling fans or even headlights come on in the process. If system voltage falls out of range, the programming procedure could be aborted with a possible loss of a controller. The other dangers are the loss of the Internet connection, a scan tool running out of power, or vehicle cabling disconnections. Any of these malfunctions will result in the loss of a new control module that cannot be returned if it is corrupted in the reprogramming process.

Figure 3

The tech at the shop provided me with a service bulletin he found to resolve a code P061B (Internal Control Module Torque Calculation Performance) and a drivability problem in the form of a throttle response issue. This is common practice today with all the resources that are now available to techs either through subscriptions from different aftermarket information companies, or directly from manufacturer websites. To verify the complaint, I hooked up the Ford factory IDS scan tool to view the codes stored in memory. There were no codes stored because the shop tech had erased them all. This is something many technicians do without realizing that if someone else were to get involved with the vehicle, there is no longer any information left behind to aid in the diagnostic process. When codes are erased, so is the freeze-frame information that can sometimes hold many valuable clues to what conditions were present when the problem occurred, thus aiding in the solving of code-related problems. Luckily, the tech at this shop was smart enough to write down all the information in detail (Figure 3). That was impressive!

Figure 4

After reading the codes he wrote down, I proceeded with reprograming to provide him with the latest updates available from Ford for this vehicle. I followed the step-by-step procedure with the Ford IDS tool, and when the programming process was done the scan tool cleared codes. This is done to assure that any “U” codes that were created in the other controllers in the network when the PCM went to sleep during the reprogramming phase are removed. The final step was to shut off the key and then turn it back on to reboot the new PCM software. I then started the vehicle, but it did not run very well and the MIL/Check Engine light came back on. When I went back into the codes menu, the same code P061B had reappeared in memory (Figure 4). The software update I installed addressed this code (as you can read in the service bulletin link 07-23-07 for this situation) when I highlighted it at the upper left side of the IDS screen (Figure 5), but the software update did not resolve this vehicle’s issue.

Figure 5

At this point, the tech knew he had made a bad decision to opt for reprogramming as a cure for the problem, but it is not uncommon for this to happen. There are many times when there are software updates intended to address particular issues on a vehicle, but this should be the last step to take after you have exhausted all other possible causes of the problem. Today, I had arrived as a software salesman only, but it was now the shop’s choice to allow me to take off my salesman’s hat and put on my diagnostician’s hat.

Figure 6

Code P061B deals with any correlation problem between the Throttle Position Sensor and the Mass Air Flow sensor. The engine had a hard time revving up, and it was blowing a lot of black smoke out of the tail pipe — it was being over-fueled. The most common cause of this condition would be a MAF sensor out of range. I needed to verify MAF operation by doing some simple data integrity checks. I placed the MAF, rpm, and TPS parameters in a graph mode to view what the PCM was seeing (Figure 6). Looking at data PID values changing in a digital format is not what I would prefer to do unless I were a number-crunching pro. Graphing signals is a major asset to diagnostics because it gives a technician the visual associations between PIDs over time to help better see what is happening. Viewing the graph you could see that the MAF was well out of range at 129 GPS at a given value of 1371 rpm with only a 26% throttle opening. It was a no brainer as to why the vehicle was running so rich that it was blowing black smoke. This vehicle had a MAF sensor that was out of range. Or, was it?

Figure 7

Figure 8

One of the cool features of the Ford IDS scan tool is that it will tie into service manual information on a code. By simply highlighting the code in the upper left-hand corner and scrolling down, the information window on the right-side screen displays the details of what can set this code (Figure7). Ford says that if you encounter a code P061B, you should inspect for an improperly-sealed air box or air filter, which can result in inaccurate measurement by the air flow sensor.

Figure 9

In addition, Ford claims that if water or snow contacts the hot wire element of the MAF sensor, it may cause a spike in air measurement. This is all good information, so at this point I needed to dig into the filter housing to check the integrity of the sensor assembly and its connector feed circuits prior to throwing a new MAF sensor at the problem. When I pulled the air cleaner cover off, I was surprised to see part of the air filter missing (Figure8) — the bullet-shaped cone. Then I inspected the MAF sensor and was shocked to see the missing air filter bullet jammed into the MAF inlet (Figure 9).

Figure 10

I removed it from the MAF housing (Figure 10) to clear the passage, put the air cleaner housing back in place to prevent any cross-flow air from passing over the sensor, and started the engine. Now, it ran like the powerful Triton it claimed to be. I re-checked my data graph, and could now see that the MAF sensor read a normal 25 GPS at a given value of 2,489 rpm at about a 20% throttle opening (Figure 11). This poor engine had had a serious air volume flow problem. This air filter speeding bullet had an adhesive failure (Figure 12), flipped over, got sucked through the filter element, and jammed itself into the MAF housing. This created a venturi effect and allowed a rush of air to flow past the MAF’s sensing device, which falsified the sensor signal. This is a rare thing to happen, but it teaches us two lessons: Beware of cheap, off-brand parts, and always check the basics before you move on to reprogramming, or any other high-tech procedure!

Figure 11

Figure 12

2000 Nissan Maxima ECM damage

1. You may come across a 2000 Nissan Maxima with 3.0L engine experiencing a low or high idle condition. This may even be accompanied by a CEL lamp with a code P0505. Remove the IAC valve and ohm out all 4 coil windings to make sure they are not under 20 ohms. If so, then the ECM most likely got damaged. Open the ECM and inspect for a burnt IC chip on the circuit board (rectangular upright chip). Usually when the ECM is opened you will be able to smell the burnt chip.

2001 Chrysler PT Cruiser CKP Damage

2. You may come across a 2001 Chrysler PT Cruiser with a 2.4L engine setting codes P0320 and P1391. This may be followed by an intermittant hard start or no start condition. Take a close look at the crank sensor to see if engine oil has not penetrated the sensor and damaged the wiring insolation at the crank sensor connector. This could lead to a shorted crank sensor signal line or feed line.

John Anello of Autotech on Wheels teaches TST technicians ten different case studies for diagnosis.

It was a rewarding experience going with John for the day.  We covered nine repair  shops. Detectives should be as good as John, for he wasted no time in pin-pointing the problem in every vehicle he came across. He used his knowledge and hi-tech tools to the max!! I was very impressed.

Sincerely,
Ed Smith

Editor’s Desk

-Joe Woods (Technical Editor, Import Service Magazine)

A scant  few years after I started making my living as a mechanic, I became pretty sure I was the best wrench around, able to solve problems nobody else could and repair cars and trucks so that the problem, at least, never occurred again. I was wrong, of course, but I didn’t find that out for a couple more years.

Most of us, in our heart of hearts, suspect the same thing for a good part of our working life. After all, we don’t really know that many mechanics’ work if they aren’t at the same shop we are. We do all our own work, after all, and only see other people’s mistakes. As I started writing more articles and meeting more mechanics, I came to realization that there were occasional people, in fact a lot of them, who could give me a real run for the money.

A year or two ago I wrote an article in Import Service magazine about John Anello’s unusual automotive business, diagnosing only the most difficult of cars, those other shops had given up on – and all of it on a payment-only-after-success basis. I followed him around one day while he went through a dozen cars, figuring out almost all of them. He is, in plain words, the most amazing diagnostician I’ve ever seen, partly from the experience of doing that most of the time and partly from his own 100-mph disposition and a good head.

There may be somebody somewhere who is faster than he is, or there may be someone with a slightly higher batting average. But I doubt there’s anybody with that combination of speed and accuracy. So I was very honored when he asked me to read thru his instruction  book and make suggestions. Except for editorial suggestions, the book is entirely his work; and fascinating work it is, drawn from the daily nightmare puzzles he solves one after another.

The cars he sees are not clean, factory fresh jobs or engines on a display stand. These are the same kind you see, complete with rust, previous amateur repairs and other mistakes, multiple problems and general neglect. As he says in the title, this instruction is “real world,” with all the grit and nicks and dents you’d expect to find in a couple hundred cars from New Jersey.

While John is an engaging writer and makes his points clearly, this is not an easy-reading, coffee-table book. There’s no fat in it and no slackening off the fast pace, so if you drift off, you’ll miss something important. He wrote the book to accompany the diagnostic course he has prepared and has given now several times on the East Coast, but the book can also be of interest and use to people who can’t take advantage of the course. There is probably more real- world automotive diagnostic  information in fewer words and pages here than in anything else you’ll find to read.

I recently attended John Anello’s One Day Boot Camp and was impressed with his diagnostic methods. His approach to diagnostics is straight forward using a repeatable method that focus on gathering as much information as possible. His techniques can be applied to almost any diagnostic situation. Take a day or a week and learn John’s techniques. Your time will be well spent.

-Norm Ouney

Hi John,

Now that I’m back to work and caught up a little, I just wanted to let you know how much I enjoyed the week I spent with you. I also appreciate the opportunity to attend the STS meeting. John, I want you to know that I have a great deal of respect for you as a businessman and a diagnostician. I watched you do a steady stream of nothing but the toughest problem cars and you handled each case confidently and professionally.

By observing your approach, I picked up some great techniques that I now apply to drivability diagnosis. You’re strategies are focused and precise, and designed to eliminate wasted time and effort while arriving at a correct diagnosis. I appreciate your candor in regards to which tools really work and which don’t. I also admire your business ethics and sense of commitment to your customers and STS Chapter.

In closing, I would say that I consider you a credit to our profession, and I would certainly not hesitate to recommend your “Boot Camp” experience to any technician wanting to better their skills.

Best wishes, and Happy Thanksgiving to you and your family!

Best Regards,
Tom Annis