Heat-Damaged Harness Causing P1860 Code – 4L80E

By Randy Peterson, Diagnostician

peterson-randyRandy has worked for Certified Transmission for over twenty four years and is an ASE Certified Master Technician, including L-1. He has been in the automotive industry for over 30 years.

1999 Chevrolet C30 7.4L 4L80E

The subject vehicle that was fitted with one of our remanufactured transmissions 6 months prior showed up at one of our repair locations recently, with the customer concern of an intermittent bumpy 1-2 shift, and a low power lugging sensation along with a CEL on. While performing our initial evaluation, we found a P1860 code stored in history, but not current. During the road test the truck was working well with no clear signs of what set the DTC, but after several minutes of driving it then started to act up. The TCC was applying right on top of the 1-2 shift, but according to the scan tool data, was not being commanded on by the ECU.

To diagnose the issue, a wiring diagram and a code description were printed and reviewed; this is a typical circuit for a GM transmission. The fuse feeds power to the transmission shift and TCC solenoids through pin ‘E’ at the case connector, and the power then runs through the solenoids and back to the VCM. The VCM is responsible for grounding the circuit to energize the solenoids. The TCC solenoid in this application is a PWM type and the computer duty cycles it on to provide a smooth engagement. A comprehensive battery and charging system test was performed to make sure that there was adequate voltage for proper circuit operations.

With this knowledge I decided to first check to see if there was B+ at pin ‘7’ (brown wire at the C2 connector of the VCM) with KOEO. [FIG 1] If there wasn’t any voltage drop at that location I knew the circuit was complete with no opens or shorts to ground, and if there was a voltage drop I would start backwards from the VCM to look for an open/short in the circuit. There was B+ at pin ‘7’, so I hooked up my scope to test the circuit with the scanner using the bilateral controls and then drive the vehicle to see if the problem would occur.


Figure 1

I back-probed pin ‘7’ at the VCM to monitor the voltage with my scope lead, and then I put an amp clamp around the brown wire to monitor amperage [FIG 2]. Using the Tech2Win software to cycle the TCC solenoid, I could see the voltage drop to 0 and the current went to approximately 0.8 amps. The specification for the solenoid is 10-15 ohms. Using Ohm’s Law I could quickly see that the amp reading was close without pulling out my calculator, at least close enough that it would not trigger a code. Now it was time to run the cables into the cab and go for a test drive.


Figure 2

After driving a couple of miles the engine temperature was up and the TCC came on. The pattern was picture perfect. The VCM cycled the PWM solenoid and then completely grounded it to apply TCC fully. The amperage was what I was expecting to see [FIG 3].


Figure 3

It took quite a few more miles before the incident recurred. I took off from a stop, shifted to second and TCC was fully applied. I looked at the scope and saw that the voltage was very erratic but near zero, the amperage was at zero and the DTC also set. How could the voltage be at zero with the TCC is on, and there is NO Amperage going through the circuit? [FIG 4] Smarter men than I would know the answer to this right away. I just could not wrap my head around it at the time. Solenoid on, TCC applied, no current flow. I had to sleep on this one.


Figure 4

The next day Carman (shop Diagnostician) and I were discussing how there could be a completed circuit, the TCC solenoid on, TCC working and no amperage in the circuit. We were ready but not willing to replace the VCM. We then noticed a harness at the rear of the engine lying on the EGR tube. We lifted it up and used a mirror to see if it had burnt through, and it had [Fig 5].


Figure 5

We determined this was the main harness to the transmission and our TCC control wire was in there. We strapped the harness up and away from the EGR tube and went for a drive [FIG 6].


Figure 6

The transmission and the TCC worked flawlessly. Carman then dissected the harness and found our brown wire was burnt and shorting to the EGR tube. [FIG 7]


Figure 7

After a few minutes of thought, the mystery in my mind was solved. There were supposed to be a couple of harness retaining clips that held the harness up off of the EGR tube that were missing/broken that allowed the harness to come in contact with the EGR tube. There was also still enough wire insulation left that when it cooled off the short to ground was not present until the EGR tube got hot enough to melt through the insulation and bring the circuit to ground. So why did the circuit ground, solenoid function, TCC on and no current detected in the circuit? It was my current clamp placement! The circuit was completed at the EGR tube from the fuse instead of the VCM supplying ground. My amp clamp was outside of that circuit, as I had placed the amp clamp very close to the VCM connector C2. The VCM in turn would not ground the circuit because the code had set once the brown wire touched the EGR tube and no longer sensed voltage at the VCM. Had I used a fuse buddy loop and had the amp clamp at the fuse box, I would have seen the amperage when the wire shorted. At that point I could have certainly condemned the VCM for randomly grounding the circuit and I would have been very wrong. Sometimes it’s good to be lucky.

Note: Someone, a.k.a. me, did not zero his amp clamp on some of the scope captures. That is why it looks like it is below 0 amps.

Don’t Be Fooled By The Tool

By Barry Bartlett, Diagnostician

bartlett-barryBarry has over 45 years of automotive experience. He has done everything from managing, owning, and operating his own general repair facility to working in the transmission industry. He’s an ASE Master technician with L1 advanced level diagnostics, the highest level of certification available. Barry and his wife Janet have been married over 40 years and are proud parents of 6 children and 26 grandchildren.

An ASE Quiz (not an official ASE test question)

A 1998 Mustang GT “shifts good” through all gears and has converter lockup, but the speedometer is dropping out after driving a short distance. The scan tool shows that there is a VSS signal and reads correct speed when the speedometer drops out. There was a code in history for the VSS but after clearing it did not return.

Technician A says it is a problem in the instrument cluster because it continues to shift properly, and the VSS signal shows correct speed. Technician B says that the computer may be lying to the scan tool and the signal could actually be dropping out. Who is correct?

(A) Technician A

(B) Technician B

(C) Both technicians are wrong

(D) Both technicians are correct

A customer showed up to one of our retail locations with a very clean 1998 Mustang GT, and the vehicle had no 4th gear, burnt fluid, and a P0734 code. Nothing else on the evaluation had raised any red flags; the car was in really good shape and very well cared for by the owner. The car was 100% stock with no modifications which is really kind of rare for most of the vehicles of this type and age that we see. It was recommended to the customer that we install one of our remanufactured transmissions, based upon our evaluation. The vehicle owner of the vehicle requested that we build the transmission from his car instead of exchange, as he was the second owner and wanted to keep the car “factory”. Honoring his request, we pulled the transmission and sent it to our remanufacturing facility.

We received the unit back completely remanufactured, dyno-tested, and ready to install back into the vehicle. With the transmission installed and road tested everything was working very well and we delivered the Mustang back to the proud owner.

After a couple of months, the customer returned with a complaint that the speedometer would drop out intermittently after it had been driven for a period of time, so I hooked up the Verus Pro scan tool and went for a road test with the car until the speedometer quit working and observed that the VSS continued to show the correct speed on the scan tool. I noted that the transmission did not seem to have any shifting issues while this event occurred.

A look at the wiring diagram showed that this vehicle had both an Output Speed Sensor (OSS) and a Vehicle Speed Sensor (VSS) on the transmission. The wiring diagram also revealed that the OSS circuit connects to the PCM, and the VSS circuit connects to the PCM, speedometer, and cruise control system. A test drive with the cruise control activated at the time that the speedometer was working revealed that the cruise control was inoperative, so that could not help in diagnosing the issue.

The question: was the speedometer bad, or did the speedometer lose signal? If it was the latter, was it the VSS circuit or the VSS itself causing the loss of signal? The instrument cluster was easy to pull out, so a few screws later and the cluster was out and our lab scope was connected to the speedometer signal wire from the VSS. During the second road test I observed that when the speedometer dropped out, the signal that we were monitoring with the scope from the VSS also did so, but the VSS showed correct values on the scan tool with no code set.

Now I was thinking: what would be the easiest way to locate the problem? Could it be a wiring issue or the VSS? If it was the VSS, why did the computer continue to show a correct speed? I then wondered what would happen if I disconnected the VSS and drove it; would it still show correct VSS speed on the scanner? I put the car on a two-post lift and disconnected the VSS. With the VSS disconnected, the correct speed was displayed on the scanner and the transmission shifted through the gears correctly.

Looking at wiring diagrams for later model years of the Mustangs, I noted that the VSS had been eliminated and the PCM was calculating the vehicle speed from the OSS signal, so on this 1998 Mustang it must have been doing the same thing, but not yet eliminated from the system. The only function of the VSS on this application was for the speedometer and the cruise control.

The graph on Figure 1 shows the signal from the VSS and Figure 2 shows the signal from the OSS which the computer is converting for the VSS reading.


Figure 1


Figure 2

After some further diagnosis on the VSS circuit, I determined that it was the sensor itself that was dropping the signal. After the VSS was replaced, the customer had no more issues with the speedometer and we had a happy customer that would recommend us to his friends.

The conclusion: the PCM can sometimes give false information to the scan tool, and therefore is not a foolproof way of diagnosing a vehicle. It cannot be solely relied upon for diagnosis. The scan tool will only point us in a direction to explore and we must investigate thoroughly to find the problem. A DVOM can be used at times while diagnosing, but you cannot see the signal integrity or erratic signals with a DVOM as you can see with a lab scope. A lab scope is a must when it comes to testing computer systems because it lets you see what the computer is seeing as well as how it is controlling electrical components. As it turns out, “Technician B” is the rock star.

Make Use Of All Available Technical Resources

By Daniel Skinner, Diagnostician

Daniel is a Diagnostician for Certified Transmission’s Blue Springs, MO shop.

When diagnosing today’s complex vehicles, we have a wealth of information at our disposal. How we use that information is crucial in making the correct diagnosis the first time, every time. In some cases the diagnosis may be cut and dry (fluid is burnt, the pump is whining, and the vehicle will not move). In other cases, the diagnosis may not be as easy, or worse; we may “think” or “assume” we already know the problem.

One of the most useful, yet easily overlooked pieces of information is the use of TSBs. Unless it is a “cut and dry” diagnosis, referring to TSBs should be routine in your everyday diagnostic practices. I cannot begin to count the number of times this has helped me by pointing me in the right direction, and even kept me from making the wrong diagnosis completely.

A perfect example of this came into the shop recently: The vehicle was a 2007 Toyota Camry with a U660E Transmission. The customer’s complaint was that the car had a 2-3 shift flare when cold. I was able to perform our initial evaluation about an hour after the vehicle was dropped off. When road testing the car, I felt NO 2-3 shift flare. In fact, the transmission seemed to work flawlessly. There were no DTCs and the fluid looked brand new. My next step was to let the car set overnight. Upon driving the car the next morning, the 2-3 flare finally showed itself, but only on the first two 2-3 shift cycles and within a mile the shifts were back to normal.

I continued on with the evaluation by conducting a battery/charging system test, voltage drop test on the ground side of the system, undercar inspection, and a more thorough inspection of the engine compartment, looking at wire harness routing and see if I could tell if any previous work had been performed. I then let the car set outside and cool back off for the rest of the day. Just before close, I took the car out once more and reconfirmed the same symptom of a 2-3 flare on cold startup/driving.

At this point, I am assuming there is an internal mechanical transmission problem occurring. A five minute search of TSBs quickly changed my mind. Toyota TSB TC007-07 describes possible shift flares on 2nd to 3rd and/or 4th to 5th within the first ten minutes of operation.  A TCM reflash is advised by Toyota to resolve the condition.

After updating the TCM calibration through Toyota’s TIS Techstream (fig.1), and performing the shift re-learn procedures, I let the car cold-soak overnight. The next morning’s test drive resulted in perfect shifts. The 2-3 up-shift flare was gone and everything was working well. Just to be safe, I let the car cold-soak two more times, each time the transmission worked flawlessly. Needless to say, the customer was elated when he found out he did not have to replace the transmission.


Another good example was on a 2008 GMC Sierra 1500 4×4 with a 4L60E transmission. The customer complaint was “Shudders on the highway while maintaining speed.” While I was test driving the truck, I observed a fairly harsh vibration when the converter was in lockup, and ONLY while maintaining speed. If I accelerated, or decelerated, the vibration disappeared. Upon further investigation, I noticed that the vibration was only occurring during the application of active fuel management (AFM).

When I returned to the shop, I did a quick search of TSBs. Entering the vehicle information in both ALLDATA and Mitchell did not reveal anything that matched the vehicles issue. At this point I could have gone forward diagnosing blindly, but something was telling me to keep looking. I don’t know why, but I just must have had one of those “gut instinct”-type of things going on, so I kept searching, and lo and behold I found what I was looking for: GM bulletin (PIP4371A) regarding harsh TCC vibration in active fuel management V4 mode.

This bulletin states that TCC slip should NOT remain at “0” when applied, but should increase to 20 RPM or greater. If TCC slip remains at zero RPM, this indicates a problem with regulator apply valve (380). A second test drive, while monitoring TCC slip, proved this to be the problem. TCC slip was at zero (fig.2), not allowing a “cushioning” effect to dampen vibrations caused by cylinder deactivation in active fuel management V4 mode. Now this is not technically a “TSB”; it is an unpublished bulletin from GM referred to as “Preliminary Information” that, as far as I know, is only available with a paid subscription to AC Delco TDS Service Information website, but can also be found on Identifix.


The customer elected to replace the transmission as advised, and the vibration was no longer present after the unit was replaced. In this case, I was able to pinpoint the exact problem by simply doing a little bit of searching, and using a scan tool.

These are just two examples of how TSBs have assisted me. I adopted using a “TSB search” in my diagnosis routine several years ago. I cannot begin to count the times that it has helped me. In many cases, the manufacturer has done the hard work for us, especially regarding odd problems, or problems we have not yet seen on later model vehicles.

In our business, the saying “time is money” is heard over and over again. Either of the two vehicles I have discussed here could have taken hours of driving, speculating, and even major disassembly just to pinpoint the problem. That is usually a very difficult sell to a customer. In both of these cases I spent no more than thirty minutes searching, finding, and verifying what I was looking for. None of us know all the answers, but there are vast resources for us to access. The correct utilization of the information we have available to us separates us as professionals. It also creates loyal customers who are confident in our professional abilities.

Don’t Ignore The Obvious Issues

By Dan Frazier, Diagnostician

frazier-danDan has been in the automotive industry for over thirty years and is an ASE Certified Master Technician. Dan has a college background in electronics engineering and specializes in diagnostics and computer controls for Certified Transmission.

I’ve always loved cars and knew from an early age, that I wanted to be a mechanic when I grew up. Well, I haven’t grown up, I’m not a mechanic – I’m an automotive technician, and I’ve been fortunate to have able to see the progress of automotive technology over many years. The evolution and integration of computer controlled components and their speed and accuracy has and will continue to change the challenges of diagnosing these systems.

How we go about diagnosing electrical and computer problems all depends on what rolls in the door, but the same basic strategies can be applied to just about anything with 4 wheels and a battery. That being said, you have to take into consideration your resources, capabilities, tooling and experience to know what you can make a profit on.

The 1st step is just doing an initial evaluation on the vehicle. Does it start, run, or move? Everybody does this differently but needs to include at a minimum a fluid level check, a visual inspection, and a test drive with a scan tool. I like to take movies of the scan data in case I need to go back and look at anything – volumetric efficiency come to mind.

OK, you got paid for your first .5 for your professional opinion of what is wrong with this transmission. So what else do we need to know? Won’t move, full of burnt fluid at 175k, needs a unit, I’m OK and move on. Need to do pressure tests or electrical evaluations? That’s different. Got a 08 BMW 550i that intermittently has the transmission go into limp mode and has low voltage and communication codes in just about every module? To the dealer it goes – with the aftermarket wet-cell battery that wasn’t registered to the vehicle. Got a 2000 Dodge Ram 5.9 gas with a P0753 – 3-4 shift solenoid circuit? I’m all in. How about a 2006 Cobalt with TCM communication issues intermittently that comes from another very good shop that wants a second opinion? I’ll swing a bat at that because I’ve got plenty of resources to help me deal with issues like that.

So what are your resources? O.E. and aftermarket scan tools, service information from various providers, information from professional trade groups, and personal experience in the field to name a few. I have access to some O.E. Scan tools and reprogramming, but BMW isn’t one of them. I also have your standard service information providers, and it seems a lot of information is very limited on Euro stuff. I have a lot of experience in electrical diagnostics, but again, very weak on Euro and very strong on domestic car lines. That’s why the BMW left and the old Dodge truck and Cobalt stayed.  Everyone has strong and weak points – take advantage of your strengths and try to learn more on your weaknesses.

So let’s talk about this fine 2000 Dodge Ram with the P0753 – 3-4 shift solenoid circuit, after seeing this on my initial inspection.

Figure 1

Figure 1

I recommended 2 hours of diagnostic time. I’m pretty used to seeing bungled up wiring, usually caused by rodent damage or bad installs, but wasn’t sure where this diagnosis would lead me. I knew how to fix the duct tape on the TV cable though. The code was set for a specific circuit and I had a good idea where I would need to go with this. One of the 1st things I considered was this was a circuit code as opposed to a performance code.

If I have a circuit code, the controlling device has detected an electrical issue, like a short or open, rather than a failure to respond to a command. Failing to respond to a command would usually result in a performance code. The module in control doesn’t see the expected results from the command but sees no issues electrically. The computer can be applying a clutch pack, VVT solenoid, fuel injector, or whatever – and it knows what changes it wants to see under certain conditions. This will help to lead you in what direction to go. If I have a circuit code, I’m busting out the electrical diagnostic stuff. If I have a performance code, I may be checking pressures or other data on the movie I took while on my initial test drive.

OK, I’ll spill the beans early; it’s another Chrysler with a bad PCM. After seeing the multiple butt connectors on the injectors, I was really thinking wiring damage was part of the problem, but I went after what the PCM was seeing to set this code.  The PCM is seeing the wrong voltage on the 3-4 shift solenoid circuit when it’s commanding the solenoid on or off. On this particular transmission, electrical diagnosis is fairly easy, as there only a few electronically controlled devices – the pressure control solenoid, TCC solenoid and the 3-4 shift solenoid.

Figure 2

Figure 2

We can see B+ supplied to the transmission from the Transmission control relay to the solenoid pack at pin 1. If I had an issue with the power supply to the solenoid pack, I likely would have seen codes for the other solenoid circuits or transmission relay stuck on or off. Ground for each circuit is provided by the PCM. So I can easily check total circuit resistance by removing the transmission control relay, and measuring the resistance between pin 87 of the relay and the control pin at the PCM. I had 28 ohms; spec for this circuit is 20 to 40 ohms, so I felt I was good there. Easily from there, I can check for a short to ground (which there wasn’t), or to power. Now, with the transmission being in limp mode, it shuts off power to the transmission control relay, so you will have to supply power to that circuit by activating the relay with a scan tool, or by using a fused jumper wire or relay bypass and check voltage at the PCM control wire. With power supplied to the circuit, I had close to no voltage at the PCM control wire when the solenoid was commanded off, where I should have close to B+. Unplugging the connector to the PCM gave me a reading of battery voltage at the PCM connector, proving the PCM had an internal short on the 3-4 shift solenoid circuit. A used PCM and a TV cable (remember the duct tape?) and this one is out the door.

BTW, the story behind this particular vehicle is a comedy of errors so to speak. A young kid bought this truck knowing it had a transmission problem – stuck in limp mode. Took it to 2 different shops and was told it needed a solenoid, or some other misinformation that I don’t know. Bought a new transmission, installed it and had the same problem as before. It took less than a half hour to reach the correct conclusion as to what was wrong with it.

Ok, we made a little bit of money on that diagnosis. What about this 06 Cobalt with intermittent TCM communication issues? We’re going to fix this one by using a kind of different approach. Resources and experience is going to be the key on this one.

We had a very good wholesale customer wanting us to take a look at this Cobalt that intermittently (several times a week) the transmission would go into limp mode and then be OK after the key was turned off and restarted. The shop had already replaced the TCM and flashed it to the latest calibration.

I’m a big fan of the IATN website, (International Automotive Technicians Network), and have used it’s database, waveform library, and forums to expand my knowledge and help me gather information about a lot of issues I can use in my everyday routine. If you have Identifix, there’s a link to IATN on the home page. Some time ago, I had come across a discussion in the Technical Discussion Forum about the use and issues that aftermarket devices such as insurance dongles, remote start systems, etc., can have an effect on communications, driveability, and transmission operation on GM vehicles. It gives a pretty detailed list of codes and symptoms that can be caused by such devices. If you want to view it, it’s in GM Tech Connect from Feb 11, 2013.

Anytime I get a vehicle in with communication issues relating to the transmission, one of the 1st things I look for are any added switches, LED’s, or anything that would indicate a non-O.E. device being installed. Another good thing is to take a quick peek under the trim panel below the steering column. If you find something like this, you might want to remove it and see if your issue goes away.

Figure 3

Figure 3

On this Cobalt, I found a wire tapped into the hi-speed CAN circuit that was intermittently causing a communication error. This picture isn’t from the Cobalt (clutch pedal?) but gives you an idea of what to look for. And while you’re looking, be especially wary of those dang Scotch-locks that seem to be so popular. Once you cut into a wire, the damage is done and it can be very difficult to trace a wiring issue down after the fact.

Expanding your knowledge base and resources is often crucial to your success and sometimes doesn’t cost very little if anything at all. Talking with other shops, technicians, networking with other professionals through electronic media, and sharing with others is almost necessary today to keep at the top of the pack.

Undesirable Effects of Dodge RAM Front Suspension Modification

By Larry (LJ) Porter, Diagnostician

porter-ljLJ has worked for Certified Transmission for over 20 years and is an ASE-certified technician in transmissions, transaxles, manual transmissions, steering, suspension and brakes. He was a remove and replace (R&R) technician for 6 years and has been a diagnostician since 1996.

One of our regular customers brought in their 2006 Dodge Ram 1500 4WD with a 5.7L engine mated to a 545RFE transmission. The owner’s concern was a very bad shake when accelerating while having the 4WD engaged.

I proceeded with an evaluation of the issue. We have detailed procedures for this process, including but not limited to a battery/charging system analysis, complete module scan for DTCs, road test, visual inspection, and TSB search. During the road test I was able to duplicate the customers concern. On acceleration in 4WD, the truck had a pronounced wobble, or shake. When the truck was driven in 2WD the concern was not there, eliminating some of the possible causes for this issue. The under-car inspection did not reveal anything that I would consider abnormal for the age and mileage of the truck. The fluids in the transmission, transfer case and both differentials were in good condition, but the front differential was a bit low due to a small axle seal leak. However, no clues as to what could be causing the issue.

There was some evidence that someone had worked on the front differential previously, or at least had removed an axle. The customer has had several other vehicles into our shop before and we had a good relationship with him so I had the manager call him and see if there had been any other work done, especially to find out if anyone had tried to repair the truck for the shaking problem before it came to us. From that phone call we learned that the truck was purchased at auction about 30 days prior to the shop visit, and therefore had no known previous repair history.

After the customer consented to some diagnostic time, I decided to start with the easiest thing I could do and removed the front driveshaft. Both the single front U-joint and the double cardan joint felt fine with no binding or play in either of them, so I left the shaft out and went for another road test. With the front driveshaft removed the wobble was gone, even in 4WD. I fully expected this since there was no load on the 4WD components.

Once back in the shop, the truck was placed onto a two-post lift so the front end components could be examined with the suspension unloaded. I will start with saying that this truck was not in perfect condition, and while inspecting the front end components there was a little bit of play in the tie rods and the pitman arm. While not very bad, it was still something that I could not rule out 100% at this point. I checked the tire circumference with a stagger gauge and it checked okay. Prior to removal of the front driveshaft, I had also driven the vehicle in a straight line while in 4WD with no evidence of any type of binding concern, so I knew that I wasn’t dealing with a gear ratio difference between front and rear differentials.

Getting back to the wobble, I can best describe what I felt as similar to a shake or vibration caused by loose front inner CV axles in a front wheel drive vehicle; when the inner CV joints get loose it can cause side to side type of sensation that we usually refer to as a “wobble”. This truck felt very similar to that, but since this is a 4WD vehicle and power is supplied to both front and rear, there is just enough difference in the feel that I was hesitant to condemn the CV axles as the culprit. While there were a bit of play in both of the inner CV joints, it didn’t seem to be enough to be the cause.

I sent an email to some other diagnosticians within our company to see if someone had dealt with a similar situation. The responses I received targeted either front-end steering components, or a bad axle. While I was waiting for response from my fellow associates, I rotated the tires front to back to see if I could “move” the sensation but yet again was unsuccessful in pinpointing the cause.

Since I could feel some play in the inner CV joints, I decided to replace both of them with reman axles from one of our parts suppliers. Yes, you guessed it…the wobble was still there. I don’t think it changed even a little bit. Disappointed but undaunted, we reinstalled the customer’s original axles back into the truck and continued the diagnosis.

Fortunately around this time we had another 2006 Dodge come into the shop, but this one drove fine in 4WD with no signs of a wobble or vibration like the problem truck had. At least now I had something to compare our subject vehicle to. We only have one drive-on lift available in the shop, so it was hard to do a side by side comparison of the two vehicles. Nonetheless, I still could not really see a difference in the CV axle angles or driveshaft angles between the two trucks, but I was still convinced there had to be something I was missing. Since there was some play in the pitman arm and tie rods we replaced those parts and had the truck aligned at a nearby general repair facility, but yet again did not fix the problem.

When I returned to the shop I parked the truck in the back lot alongside the other 2006 Ram and went in to speak with the manager to tell him the news. I am really frustrated at this point because I am having difficulty fixing this truck. When I go to the back lot to test drive another vehicle I look at my nemesis sitting there and I noticed something: the front end of the problem truck is sitting a couple inches higher in the front as compared to the truck that does not have the issue. Neither of these trucks has a lift kit installed, but both have stock-sized tires; so why is the ride height different?

I took a closer look at the front springs and noticed that there was more space between the spring and the upper spring perch on the subject truck than on the comparison truck.

I do a little research and find that there are companies selling a “leveling” kit for these trucks that is just simply a block to increase the installed spring height intended to raise the front end ride height, but without addressing the increased front CV shaft angle.

Now, to answer the question: why does this have such a big effect on the way the truck drives when it only adds a couple of inches to the ride height? The differential is attached directly to the motor mounts and moves with the engine. Because of this, the differential rotates upward on the passenger side when the engine’s torsional forces are active upon acceleration. This, combined with the increased CV angle from the spacers (without a differential drop), causes the CV joints to bind under a load.

We removed the “leveling” kit which should be renamed to, “Change your driveline angle kit”. Predictably, the wobble was gone and the truck drove like new again; well maybe not new, but you know what I mean. It’s worth mentioning that there are other brands of leveling kits available that will raise the front end of the truck the correct way to get rid of the factory rake these trucks are built with, yet do not change the driveline angle. These kits are more $ than the $50.00 – $100.00 kits, but the results would be well worth it. This is just another example of how aftermarket parts can deal us fits!

Volumetric Efficiency Helps Pinpoint MAF Issues

By Chris Adams, Diagnostician

adams-chris-2Chris Adams started with Certified Transmission in 1986 as an R&R technician, and currently works as our Diagnostic Trainer. His current duties involve training and advising our retail diagnosticians, as well as assisting in the research and development of our remanufactured products. He also holds ASE Master and L1 certifications.

For this installment of R&R Tech I would like to take some time to discuss how engine performance can affect the transmission operation. We have all heard it before; the engine must be running properly in order for the transmission to function correctly. What “properly” mean in this scenario? We all use different terms when we tell the customer, “You need to get the engine running properly”, or good, correct, better, whatever terms we use; in our mind it all means the same thing. We either see or feel something that is not right with the engine performance and to try to protect our investment (our remanufactured product) by telling the customer that it needs to get repaired in conjunction with the transmission replacement. How far do we need to go with this? Just tell the customer and leave it up to them, or do we require them to have it checked/repaired and return it to us for inspection?

I suppose it would depend on the severity of the issue, but for the most part we require that the customer return the vehicle to us for verification of repairs. One of the easiest things we deal with is a simple DTC related to a sensor issue, for example, an O2 sensor code. We can make sure that the code has not returned, check Mode 6 data, and make sure that the monitor has completed. There are others that are a little more difficult, perhaps more time-consuming for us to verify. This is one story that I feel is a perfect example of this and why it is so important that everything with the vehicle is in proper running condition.

Our test subject: a 2006 Chevrolet K1500 with a 5.3L engine and 4L60E transmission. This vehicle arrived at one of our facilities with a 2-3 neutral condition. We installed a remanufactured transmission, re-programmed the PCM, and road-test. Everything seemed to work well: engine running fine, no DTCs, and fuel trims are less than 10% total. Everything looks good so we deliver the vehicle to the customer.

About 10 months and 12K miles go by and the truck returns with really poor shift quality. The transmission slides through the 1-2 shift and flares on the 2-3 shift. The fluid has somewhat of a burnt smell to it, and now the PCM has a P0101 MAF code in it. We replaced the transmission under warranty and recommend that the MAF sensor be replaced. The customer declines the MAF sensor replacement and says that he will take care of it himself. This is where we dropped the ball. We should have pressed the issue and done the work ourselves. The customer later returned for a follow-up visit, but the Diagnostician that originally road-tested the truck was away on vacation. The Tech looks at the truck, verifies that the MAF sensor was replaced so we send the customer down the road again.

As I was reviewing warranty claims, this case caught my eye. Looking further into it I found out that all we did actually did was verify that the MAF sensor was replaced, and no one could even tell me what brand it was replaced with. I knew that I needed to have the customer return yet again for us to verify further. If we didn’t, we would risk damage to the replacement transmission.

The understanding customer dropped off the vehicle so we could do some more in-depth testing. The MAF sensor was a new one from Delphi, and the receipt was still in the truck. The cost was around $130. I knew what an AC Delco sensor costs, so that was my first red flag. The truck did seem to run okay, fuel trims are still less than 10% total, and no DTCs. The next step was to monitor the transmission line-pressure with a gauge, and PIDs with the Tech2Win laptop.

The line pressure tests at idle and stall were both within specs (ours do run a bit higher with modifications that are done inside the unit), and under normal driving conditions, everything seemed to work well. Enroute to a road with a higher posted speed limit, I performed a WOT test while in 2nd gear and at WOT I was a little concerned that the line pressure did drop a bit while pulling through 2nd gear, but just looking at the live data nothing really stood out to me.

I have been to many training seminars and one that I learned quite a bit about engine performance testing was from “The Driveabilty Guys”. There is a “Volumetric Efficiency Test” that I have used and works very well. To do the VE test, you have to make a WOT pull through a gear change whether it be the 1-2 or 2-3 and record certain data pids on the scan tool. The reason I used the Tech2Win is it has a fairly fast sample rate as compared to some aftermarket scan tools. I also make two runs under the same conditions, just to make sure that the data is valid.

This is a screenshot of engine parameters during a WOT pull up to the 2-3 shift. The cursor (small white arrow at the bottom) is stopped at max RPM of 5665, MAF reading of 202.25 g/s, and ECU calculated (scan tool data) engine load of 85%, varying between 80% and 91% through the pull.


Figure 1

These are the transmission data pids I recorded on the exact same stretch of road while under the same operating conditions. The PCS duty cycle is running at 38%, both the actual and reference current is sitting at .72 amps at WOT pulling through 2nd gear, and on the pressure gauge this was about 150psi (this does not match the pressure to current charts for a OE transmission because of our modifications to the line pressure circuit).


Figure 2

I got back to the shop to go over the recorded data and gather everything needed to use the VE calculator (there is a phone app that works well, or online versions available found with Google). The VE calculator requires the engine displacement in liters, mass air in g/s, max RPM, and IAT reading. Using the data I recorded and inputting it into the VE calculator, the two different readings I took showed 73% and 68% efficiency, where minimum spec is to be 80% I suspected that there wais a bit of MAF degragation but honestly just by driving the vehicle you probably would not notice it. I decided to buy a AC Delco MAF sensor just to test with and see if I have different results.

I reran the same tests, and honestly, I was a little bit surprised at the results.


Figure 3

This image shows the same parameters as figure 1, and the cursor is stopped at max RPM of 5651, MAF reading of 239.82 g/s, and ECU calculated load of 96% varying between 93% and 100%. Using the VE calculator, the two different readings I took showed 83% and 84% efficiency, and therefore within spec. Idle and stall line pressure readings were still the same, but during the WOT pull through 2rd gear the line pressure was 30 psi higher than before replacing the MAF sensor.

In the following image, these are the same transmission PIDs as displayed in figure 2. The PCS duty cycle is running at 32% and both the actual and reference current is sitting at .60 amps while the pressure gauge was showing about 180 psi. All these recordings were taken from the same stretch of road and the same outside air temperature.


Figure 4

The operation of the transmission was also noticeably different; the shifts were firmer, the TAP cell numbers dropped (sorry I did not save a screenshot of that), and the line pressure was more responsive in addition to the 30psi higher reading while driving it. I was really surprised that this had no affect on line pressure during the stall test, so it just goes to show that the old way of doing things simply won’t cut it in this day and age, and this is just a 4L60E!

Curiosity got the best of me, so I wanted to know if this was possibly just the result of a bad MAF sensor from Delphi. I got another brand new Delphi sensor under warranty, reran the same tests on the same stretch of road at the same (close) air temperature, and got almost the same exact results as the first Delphi sensor. I can only say that the base calibration of the Delphi sensor is just not quite right, perhaps just enough to have an adverse affect of the operation of the engine and transmission.

I am happy to say that the customer had just returned for a service and has 30k miles on it since we installed the last transmission and everything is working properly. He also stated that he noticed improved fuel mileage since we installed the OE MAF sensor and was happy that we took the extra steps to make sure his vehicle was repaired correctly. I kind of forgot about this one until he returned, so I am glad I saved the screenshots and notes from this vehicle; we use these types of examples for our own internal training.  I encourage you to try the VE testing and see what you come up with. You don’t have to do it on every vehicle with a MAF sensor, but do look at the engine load % on your scan tool and if you see one that is low, do the VE test and I can just about guarantee you will be surprised at the results.

Please keep in mind that a failed/skewed MAF sensor is not the only thing that can affect VE; clogged intake, clogged exhaust, or poor fuel delivery can also cause these same issues.

Shifting Problems Caused By Third-Party Programming

By Chris Adams, Diagnostician

adams-chris-2Chris Adams started with Certified Transmission in 1986 as an R&R technician, and currently works as our Diagnostic Trainer. His current duties involve training and advising our retail diagnosticians, as well as assisting in the research and development of our remanufactured products. He also holds ASE Master and L1 certifications.

I have covered some general concerns that have arisen from aftermarket tuning devices and software in a couple of previous articles. I don’t want to sound like I just keep repeating myself, but the problems keep coming through the doors making this an ongoing relevant discussion. I don’t know if it’s just because I am more aware of these issues and maybe look for them more than some folks do, but somehow these vehicles find their way to our shop after the consumer has been bounced around from shop to shop before they get referred to us. In this article I am going to cover one specific issue that I had ran into a few months back.

I will start by saying that getting ALL of the information from the customer is a crucial step in the diagnostic process; it can save you time and headaches if you have everything that you need from the customer before you start, and this story is a good example of this.

A 2006 Chrysler 300C shows up at the shop equipped with the 5.7L Hemi engine backed by the NAG1 (722.6) transmission. The customer was complaining about harsh coast downshifts and dropped the vehicle off with us for an evaluation. No other information was provided, and whether he did not offer additional details or if the service writer who was assisting the customer did not ask for any of the previous history of the vehicle, this was the first step where we could have done better.

Moving forward with the evaluation, we have detailed procedures including but not limited to, a battery/charging system analysis, complete module scan for DTC’s, road test, visual inspection, and TSB search. During the road test the vehicle did have pronounced, firm downshifts on the 3-2 and 2-1, but the upshifts also seemed to be firmer than desired. There were no codes but the visual inspection revealed there were some performance enhancing modifications done, mainly exhaust headers, deleted catalytic converters, and a “cold air” intake. The first thing that I would have normally done at this point would be to hook up a pressure gauge, but thanks to Mercedes engineering, we have no line pressure tap we can use for testing.

TSBs only showed one thing that was sort of relevant, but not exactly what we are after: an ECU software update for 1-2 upshift shudder and/or roughness. Not really what I am looking at, but I do know that I have had reprogrammed ECU’s before that have fixed a concern that was not detailed in the description of the TSB. At this point I am going over everything in my head before I make a recommendation on how we are going to proceed, and I have that a-ha moment: remember when I mentioned that the catalytic converters were deleted and also stated that there were NO codes? How could that be? Why were there no P0420 or P0430 for catalyst efficiency codes if there weren’t any cats? Somehow the monitors for those codes had to be turned off. Maybe a tuner was installed, but is that what is causing this issue? We needed to call the customer and get some more information.

And now, the rest of the story (as Paul Harvey might say). After talking to the customer, the vehicle did have a tuner installed, from DiabloSport [Figure 1]. Furthermore, another shop had installed Mercedes AMG solenoids (visually identified by the blue cap) that run higher output pressures than the regular old 722.6 solenoids. Both the other shops this vehicle has been to just told him that the coast downshift clunks were just a side effect of the AMG solenoids and there was really no fix, and while this may have been true, I am not one to go by anyone else’s diagnosis. I needed to find out for myself what exactly was causing the problem.


Figure 1

The customer was hesitant to spend any more money because of his past history with the other shops, given that he was not provided a valid answer to his shift issues, but I assured him that I would figure out what was causing it and what we could do to fix it. To start I wanted to make sure that this was just not some type of software issue caused by the OE programming, or from Diablo. The first step was to uninstall the tuner, and then use the Chrysler WiTech scan tool to update ECM, TCM and ABS module. I also used the Diablo update utility to get the tuner updated and reinstalled the tuner making no additional changes.

On the initial test drive all the upshifts were pretty firm, but I still had the harsh downshifts from 3-2 and 2-1 after several shift cycles the 1-2 and 2-3 seemed to get better. None of the other shifts seemed to be any different at all; was this just a case where the computer can simply not adapt to the higher output pressure of the AMG solenoids? I uninstalled the tuner again (which I probably should have done this from the start), and drove the vehicle without the tuner installed. Right off the bat the shifts were noticeably different (softer), and after several shift cycles the computer adapted the shift feel and everything (including the downshifts) felt normal. At this point I was really thinking that the tuner is to blame. One thing that we have learned over the years is to test and retest, and also to ask yourself, “Can I duplicate the problem again?” I decided to reinstall the tuner and find out if I could duplicate the problem, and sure enough, when the tuner was installed the shift feel changed and the downshift clunk returned. At this point I knew that the tuner (rather than the solenoids) was causing the issue, but why? More importantly, how do I find out why?

I have an HP tuner interface that I covered when I wrote about the 6L80, [Figure 2], so I looked to see if this Chrysler was a “supported” vehicle, and sure enough it was.


Figure 2

This gave me a way to see the details of the tune. This type of software, whether it be HP Tuners, EFI Live, or something similar is the only thing that gives this type of X-ray vision to see inside the table values of an ECU. The next step was to reinstall the tuner and hook up the HP tuner interface. After “pulling” the tune out of the vehicle and looking at the many editable parameters, something caught my eye: it was under the “adaptive” tab [Figure 3]. Was this the root cause of all of the issues? It sure looked like it could be.


Figure 3

The “Fill Time Adapt” for the 3-2 and the 2-1 downshifts had been disabled within the tuner. Also, the “Fill Pressure Adapt” for the 3-4 and 4-5 upshifts as well as the 3-2 and 2-1 downshifts were also disabled. Before I went any further, I did something I hadn’t mentioned earlier. After I had reprogrammed the vehicle back to stock programming with the WiTech, I saved the stock tune file in the HP tuner software. I opened the “stock” file and low and behold the adapt page was identical to the “tuned” file, but those same adapts were disabled also. The only thing that was different was the “Max Positive Fill Time” was changed from 240ms to 300ms [Figure 4]. Now I had to look further, but where do I start with the many editable parameters that were available?


Figure 4

The HP Tuner software has another cool feature. It has a “Compare” function where when you have a tune file open and you can open another tune file for comparison. In this example, I had the stock file and the tuned file opened [Figure 5]. Everything that is shown in green are changes that the tuner made to the stock file. This narrows down the areas where you would need to look to see the changes that have been applied. Now I know where the issue lies, and what can be done to correct it. The only question left to answer was whether the customer would authorize the repair. My recommendation was to remove the tuner and rewrite the stock tune file with HP tuner software; just removing the tuner is not really an option at this point because of the modifications to the vehicle that were made. Unfortunately, the customer declined although I was confident that we could restore his performance needs and make the transmission shifts clean, but also get rid of the annoying downshift clunk.


Figure 5

The customer wanted the ability to be able to change the tunes depending on the fuel to be used. This is something that I could not provide for him, but we might see him back again someday. For now he has decided to live with the downshift clunk. It was another good learning experience for me, though. I always welcome problems that are not the everyday things that we usually have to deal with. I do still have some unanswered questions with this one, such as why are the shift adapts for those particular ratio changes disabled? What would happen if I enabled them? Is it just that the fill time/pressure is determined from another shift change and not needed with those particular ones? I’m sure at some point I will see another chance to answer these questions reeling around in my head. Every day brings a new challenge.

Using Waveforms to Pinpoint Marginal Electrical Components

By Randy Peterson, Diagnostician

peterson-randyRandy has worked for Certified Transmission for over twenty three years and is an ASE Certified Master Technician, including L-1. He has been in the automotive industry for over 30 years.

Vehicle: 2009 Mercedes Benz E350 AWD.

Engine: 3.5 V6, Transmission: 722.6.

Customer Concern: 30-40 mph is the top speed, drive modes won’t switch, neutrals out in reverse, stuck in low gear at times, can’t shift manually, only works in drive.

Stored DTC 2767, Component Y3/6n3 (speed sensor) is faulty.

Prior to any diagnostics, I performed the initial code scan and road test. There was an unrelated engine code stored, but the DTC I was interested in was the 2767 stored for the transmission. 2767 is a manufacturer-specific code relating to the Y3/6n3 speed sensor. There are 2 speed sensors on the conductor plate that the TCM uses. Y3/6n2 is active whenever the vehicle is moving, be it forward, or reverse. Y3/6n3 is used in second, third and fourth gears.

The data PID for the Y3/6n3 speed sensor was showing a flat line and the reading was 8000 rpm with the code present (FIG 1).


Figure 1

I made all my notes, cleared the code and drove the vehicle. The transmission worked well, shifted through all the gears and showed speed signals on both speed sensors on the scan data (FIG 2).


Figure 2

After the initial road test and data gathering, I made the request to get more time authorized to perform more in-depth diagnostic testing. The call was made and the customer agreed to let us go ahead with testing.

After a short time looking for information, wire diagrams and pin out charts, I found most of the information on this vehicle was for a 722.9 transmission. This vehicle has the 722.6 transmission in it. I had to comb through several sources to find the information I needed. After printing and reviewing the information I was ready to dig into this further (FIG 3).


Figure 3

The TCM is located on the passenger side under the carpet towards the front. The nice thing is that Mercedes makes it somewhat easy to access. Pull the carpet back, locate the 3 nuts that hold the mounting plate, pull it out and the TCM is now out in the open. Locating the circuits I needed to monitor, I set up the scope (FIG 4).


Figure 4

I’m going to monitor both Y3/6n2 and Y3/6n3. These are 3 wire sensors, power, ground and signal. They make a 0.0 to 6.0 Volt square wave pattern. I attached a probe to each signal wire and grounded it to the circuits’ ground wire at the TCM (FIG 3). I also connected a DVOM to the ground wire and the battery ground to watch for voltage drop on the ground circuit. I had a scan tool connected to watch the PID data on the Y3/6n2 and Y3/6n3 speed sensors. I was watching to see what was happening when the code sets.

I started out on the road test with everything connected. My speed sensor patterns were a good square-wave pattern going from 0.0 volts to 6.0 volts (FIG 5), and the voltage drop on the ground was constant at 0.06 volts.


Figure 5

I get on the highway, shift transmission to 4th gear. In 5th gear the Y3/6n3 does not record any speed signal. I drove for about 4 miles when the Y3/6n3 signal started to drop (FIG 6).


Figure 6

It fluctuated between working and dropping to less than 0.5 volts (FIG 7).


Figure 7

What was interesting was the transmission was still in 4th gear and the PID reading was normal (FIG 8).


Figure 8

Nothing had changed on the scan tool and no DTC was set. I got off the highway and performed several stop-and-go maneuvers. The transmission was working correctly, the PIDS were normal, and the voltage was still below 0.5 volts on the scope. What in the world is going on? The sensor is malfunctioning, yet the PID is normal and the transmission still functions and shifts correctly.

I developed a theory that, even though the speed sensor voltage is very low, the computer sees some sort of action and must use the other speed sensors to maintain transmission shifting. The speed sensor must completely fail, 0.0 volts (flat line), for the DTC to set. I let the vehicle cool down and repeated the process again and got the same outcome. I still have no code and not sure why. I could not get the speed sensor to completely fail to confirm my theory. I removed the Y3/6n3 wire from the TCM connector (FIG 9).


Figure 9

The Y3/6n3 sensor does not monitor in 1st gear but starts monitoring in 2nd. There was no KOEO or KOER code because I removed the sensor return wire and not the power or ground wire. I would not see an effect until the transmission shifted to 2nd gear. TCM would still see voltage through the sensor on startup (FIG 3). If I had removed the power or ground wire I’m sure I would have set a KOEO code. As I started down the road as soon as it shifted to 2nd gear the check engine lamp came on, the vehicle jerked and the DTC set the speed sensor PID was flat line at 8000 rpm (FIG 10).


Figure 10

I stopped, cleared the code and repeated the process. I got the same results. If the code was present, the vehicle remained in failsafe and the PID read 8000 rpm. I then reconnected the signal wire, cleared the code and drove the vehicle. The sensor had the low voltage but the vehicle shifted and the PID was normal.

I was confident I’d proven my theory and recommended speed sensors (conductor plate) be replaced. The customer agreed to the repairs and we installed the new parts.

I left the equipment hooked up for the final road test. I initially drove the vehicle 10 miles on the highway in 4th gear. The sensor patterns were good, 0.0 volts to 6.0-volt square wave pattern (FIG 11 & 12).


Figure 11


Figure 12

Driving back to the in stop-and-go traffic the pattern never dropped. I was happy with the results. I removed my scope set up and put the passenger side area back together. I drove the vehicle one more time with only a scan tool connected. Again another 10 miles and everything was normal (FIG 13).


Figure 13

There were a couple difficult and confusing things about this diagnosis. First, I had a very difficult time finding the technical information for the 722.6 (5 speed) transmission for this vehicle. Nearly all the information I found was for the 722.9 (7 speed) transmission. This delayed the diagnostic process. Second, even though the sensor had virtually no signal, the transmission still operated correctly. The sensor had to completely fail for the transmission to go into failsafe. I could not find that documented anywhere I searched. It may be out there somewhere. There are too many times at the shop level we don’t have spare time, but luckily, I had enough time to perform the diagnostics, develop a theory and prove that theory.

Rodents Wreak Havoc On Vehicle Wiring

By Troy Hopp, Diagnostician

hopp-troyTroy has been in the automotive repair industry his entire career and has been with Certified Transmission since February 2010. He has an Applied Science Degree in Automotive Technology from Western Iowa Tech and is an ASE Master Certified Technician.

As I think back about all the bizarre wiring issues I have encountered over the years, there is one that sticks out in my mind. We had a 1998 Ford Contour come into the shop with a Transmission wiring harness that had been completely chewed up by mice. I mean every wire in this harness had exposed copper running the length of the harness for at least two feet in one spot, and I can recall at least 10 wires shorting out against each other causing multiple codes and drivability issues. I asked myself why this mouse (or these mice) would choose to feast on this poor, unsuspecting wiring harness? After a quick google search, I found that some car companies were using biodegradable soy-based wire insulation. They are no longer using plastic non-biodegradable wire insulation and that has to be more environmentally friendly, right? One would certainly assume! It is more than likely more economical as well. Unfortunately it is also more inviting and tastier to all the rodents of the world. What could be better than a nice cozy warm engine bay to build your nest in, and have a free meal to boot!

Well, enough talk about those mischievous mice. Let us get to the issue at hand. Recently a young lady had a 2005 Ford Taurus towed into our shop. The complaint was that it suddenly quit moving. As most of you in the transmission business probably already know, the torque converters in these cars have been known to break causing the vehicle to just suddenly stop moving. Naturally after verifying that it did not move and the odometer showing 187,419 miles, I wanted to automatically blame it on the internals of the transmission, given their long history of failure. However, I also know the foolishness of just assuming this, so some quick testing still needed to be done before condemning the transmission.  Over the years I have found the easiest and most efficient way to verify a bad transmission on a Taurus that does not move is to simply disconnect the solenoid connector, since it is right there at the top of the transmission, wide open for all to see and very easily accessible. If the vehicle still will not move then it is probably safe to assume the problem is in the transmission, or possibly a broken half shaft.

Well, guess what? My initial assumption was, well, dead wrong. After disconnecting the solenoid connector, the transmission actually went into gear and would move, indicating a possible external wiring issue. Of course this would be the case, or I would not be writing about it, right? Now it was time to grab the scanner. A quick readout of the history codes revealed a whole plethora of problems. The codes almost too numerous to list were as follows: P0300 – Random misfire detected, P0316 – Engine misfire detected on startup, P0430 – Bank 2 catalyst efficiency below limit, P0442 – Evap system leak detected, P0713 – Transmission fluid temperature sensor high input, P0740 – Torque converter clutch fault, P0743 – Torque converter clutch electrical fault, P0750 – Shift solenoid A fault, P0753 – Shift solenoid A electrical, P0760 – Shift solenoid C fault, P0763 – Shift solenoid C electrical, and finally P1744 – Torque converter  clutch system performance. Whenever I see this many random codes all in one place I start bracing myself for a blockbuster-selling horror story of wiring mayhem!

The search was on. A thorough visual inspection of the under hood wiring revealed a hidden mess of chafed, corroded, and blackened wiring hiding beneath what used to be 1 inch round plastic conduit:


Figure 1

Located between the front edge of the engine and the right side of the firewall near the right strut tower (FIG 2), the wiring harness was totally grounded out and melted against an aluminum Air Conditioning tube that had to be physically and forcibly pried apart.


Figure 2

After observing the nightmare of chafed wiring I knew would take the rest of the day to repair, I turned my eyes to see the grooves that the wiring had actually implanted into the aluminum A/C tubing like a bunch of corn rows (FIG 3). I am surprised the Freon did not all leak out.


Figure 3

After giving the wiring harness a makeover, the transmission lives to see another day. The nice young lady was extremely pleased that she did not have to buy a transmission and that she only had to purchase a wire repair plus a transmission fluid and filter change. I guess the point I am trying to make with this story is to remember that not all failures that appear to be the same are created equal, and that the same old familiar road does not always lead down a straight path. Sometimes curves appear out of nowhere forcing you to dig deeper with your diagnosis. I actually kind of enjoy the challenge, though. Challenges keep us thinking, and after all, life would certainly be boring if you had to go to work and do the same repetitive things day after day.

Oh and by the way, the rodent eating soy-based wire insulation problem I mentioned at the beginning of this article can now be easily avoided or at least deterred. Companies now offer a form of electrical tape treated with capsaicin, which is the same stuff found in hot peppers that turns chili into 3 alarm fire chili, thus deterring the mice and other rodents from having a free meal. Honda sells 20 meter rolls of it for around $36.00. The more you know…

Extra Effort Required to Pinpoint Electrical Intermittents

By Barry Bartlett, Diagnostician

bartlett-barryBarry has over 45 years of automotive experience. He has done everything from managing, owning, and operating his own general repair facility to working in the transmission industry. He’s a ASE Master tech. with L1 advanced level diagnostics, the highest level of certification available. Barry and his wife Janet have been married 42 years and are proud parents of 6 children and 26 grandchildren.

We’ve all had to contend with intermittent electrical problems. These are typically the most difficult issue to pinpoint, as the root cause literally plays, ‘Hide and seek’ with you. The following issue that I encountered belonged to a 2008 Dodge Ram 5500 in which the customer stated the transmission wasn’t shifting, and the CEL was on.

After some initial diagnosis, I noted that code P0778 was setting for the linear solenoid B electrical circuit. When this code sets, the transmission goes into limp mode and will not come out with a key cycle. The only way to get out of limp is to clear the code. The questions I always consider are what are the possible causes, and how will I test them?

I did some research on this AS68RC transmission to find out operating and circuit specs along with all the possible causes of the code. I found that there was not much information on this code other than an electrical issue and could be internal or external wiring, the solenoid, or the computer. I decided to start with the easiest thing to test, which is the wiring circuit. I like to test the entire circuit at the computer connector first so that I can see the complete circuit resistance, and if I see a problem I can narrow it down from there.

I went to pins 8 and 9 at the ‘C’ connector of the TCM and checked ohms through the circuit. The spec calls for 5.5 to 7.5 ohms on the linear PWM solenoids, and 14 to 16 ohms on the on/off solenoids. The circuit tested at 6.4 ohms, so all looked good. I compared it to linear solenoid ‘D’ with the same reading. I also like to load test the circuit which can reveal a poor connection, so I powered up the solenoid and when I momentarily grounded it, the solenoid pulled about 1.9 amps. I compared this to a draw test on solenoid ‘D’, which is also a PWM solenoid with the same specs. I then monitored resistance on solenoid ‘B’ while moving wire harnesses and connectors, and there was no variation.

After several miles road testing with no code set, my feeling was that the solenoid or internal harness was the problem, so the decision was made to replace the internal wire harness and solenoid with a new one. Chrysler sells all the solenoids together in a package, but we found that the Allison linear solenoids are interchangeable. The AS68RC solenoid ‘B’ is a normally closed solenoid, and a GM part # 29533074 can be used to replace it. The linear solenoids ‘A’, ‘C’, and ‘D’ are normally open, so they would require a different part number.

About 3,000 miles and several months later the truck returned with the same P0778 code and in limp mode. Awesome. Now we know the concern is intermittent. Since the linear solenoids are PWM solenoids I wanted to look at the pattern on screen and see what the trace looked like. So I got out our Verus Pro and went to the lab scope, but when I looked at it on the screen it just had a flat line voltage, but no PWM trace. I was puzzled by this, so I went to linear solenoid ‘D’ which in park should have the same readings, and again no PWM; just a flat line voltage.


Figure 1

I noticed that the voltage would change going from park to reverse, to neutral and to drive. The voltage in park would be about 9.5 volts, in reverse the voltage would read about 12 volts, in neutral about 9.5 volts and in drive about 8.3 volts.


Figure 2

I measured the amperage compared to volts, the 8.3 volts was equal to .630 amps, the 9.5 volts was equal to .453 amps, and the 12 volt was equal to .134 amps. The high amperage (both .630 amp and .453 amp are in the high range) would open the pressure switch #2 and low amp (.134 amp) will close the # 2 pressure switch.

I then wondered if the computer was controlling some kind of variable resistance or voltage on the negative side of the solenoid. I thought I would look at the Hz to see if I could measure any fluctuation of the signal, and was surprised to see that it was pulsing the signal at 1003 Hz and was so fast that the scope was not picking up the wave form in the signal until I set the time scale to 200ms. I went to the voltage graphing screen on the scope because it will let me see up to several minutes on the screen so that I could monitor the voltage signal on a test drive.

I monitored the solenoid and on several test drives of about 60 miles I found the right combination to get the code to set. I found that when I made a right hand turn on acceleration and hit a bump the signal on the negative side dropped to 0 volts, the P0778 code set, and the transmission went into limp mode. Finally, the truck was showing its cards. I could duplicate this same scenario several times now, so I knew what condition was causing the code to set and during all the miles of driving the voltage signal on the positive side was steady with no variance, and on the negative side it changed correctly with the commanded shifts. I determined that the problem had to be in the external harness.


Figure 3

I made an insulated pair of twisted wires to run from the computer to the transmission and secured them in place and after several miles of road testing, no more problems arose. The truck has now been gone for several months and no issues, so I can confidently say that it is now fixed.

As we would always hope, it would have been much more convenient for all had the issue been reproduced on the customer’s first visit. With intermittent problems we’re at the mercy of the gremlins, so sometimes the extra effort pays off when you know that the issue is, in fact, intermittent. That’s not always apparent the first time around.