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.

Take Time to Pinpoint: Chevy Driveline Noises Aren’t Always What They Seem

By Dana Deeke, Diagnostician

deeke-danaDana joined the Certified Transmission team in 1991. Dana has worked in all positions at the Lincoln location, starting as an R&R technician and is now our current diagnostician for our Lincoln, NE facility. He enjoys car racing and spending time with family and friends.

A while back I had a truck that came into our shop for a noise concern. The customer stated that he heard a loud clunk or repeated popping noise when he would accelerate with the truck in automatic 4×4 mode, as well as in 4×4 high and 4×4 low. He also stated that he didn’t notice the noise under light acceleration in these modes, and that the noise was not present when he was in 2wd under any type of acceleration. The truck was a 2009 K1500 Silverado with a little over 83,000 miles on it. Upon reading the description, it sure seemed like I had a transfer case problem to look into.

I started with a road test to see if I could duplicate the customer concerns, and the truck responded just the way the customer described: it would make a repeated rhythmic clunk or pop noise under medium-to-heavy acceleration that that could also be felt in the floorboard, but only in the four-wheel drive modes; nothing at all in two-wheel drive. I also noticed that even in the four-wheel drive modes, it would NOT make the noise when backing up, even under harder acceleration. I later found out that this would be one of the clues given that helped me solve this problem. This noise was fairly loud and you could really feel it in the truck when it happened, so at this point I still thought it would likely be a transfer case problem.

The first hurdle had been cleared: I duplicated the symptom! Now on to figuring out what the source of it was. I took a sample of the transfer case fluid, and while it didn’t look great, there wasn’t enough evidence to condemn the transfer case. What about the tires? Whenever I have an all-wheel drive or four-wheel drive vehicle come into the shop I try to make a habit of checking the stagger of the tires on all four corners, making sure that they are very close in actual size, not just looking at the size stamped on the tire. All of our shops have a tire stagger gauge:


Figure 1

While it is not accurate enough to provide a “tire rollout” spec, it does make quick work out of determining a stagger issue. Too much difference in circumference due to wear can cause all kinds of noise and bind up issues. These tires were 1″ different from the largest to the smallest, and really didn’t look like were rotated often if at all. I explained to the customer our findings and suggested that he start by having the tires replaced, as they were out of spec and I had seen problems with noises and bind ups cured with properly staggered tires. The customer stated that they were planning to replace the tires soon anyway so he agreed to start there. I asked them to return with the vehicle so I could confirm if it did or didn’t fix the problem.

The customer returned with his truck and I went for a drive again, going through the same procedure as before. It didn’t take long to discover that the symptom was still present. A drive-on pit at our shop makes quick work of doing a visual inspection of the underside of the vehicle. There were no obvious drive shaft problems with the front or rear drive shafts, but I did notice some slightly abnormal movement out of the passenger front axle area, where the flange comes out of the differential and bolts to the cv shaft. This would be my second clue along the path of diagnosing this noise.

I thought back to the test drive and symptoms; if it was the transfer case, why didn’t it make the noise backing up? What about that extra play in the flange coming out of the front differential? I decided to look at the front differential more closely, first by draining the fluid.

This inspection showed us signs of metal flakes that had settled to the bottom. Next, I looked closer at the axle flange:


Figure 2

I rolled the truck in four wheel drive back and forth on the pit a few times then applied a little outward pressure to the axle flange and it moved out of the differential a good half-inch, well past where it had been riding on the seal normally. There were no signs of a leak from the axle at all. At this point I recommended pulling the axle housing off the differential to inspect the parts inside.

Once I had it apart it became clear what was going on: the passenger inner axle with the flange that you can see in figure 2 goes into the differential where the splined end of the shaft connects to a collar that is splined in the center (figure 3). On the other side of the collar is a set of teeth which then mate up to a stub shaft (figure 4):


Figure 3


Figure 4

The collar also has a groove that the fork engages into. When the actuator motor pushes the fork over, it slides the collar over where the teeth on the outside of the collar engage the teeth on the stub shaft. This ties the two front axles together. When in two-wheel drive the collar is free to spin on the end of the axle shaft coming in from the passenger side.

The teeth on the collar that engage the stub shaft were really worn and had a taper on the leading edge of the teeth, and as you can see in figure 5, the mating surface is not very deep where the teeth mesh:


Figure 5

One interesting side note, the teeth on the stub shaft that mated to the teeth on the collar showed very little wear (figure 3). When there was a load applied to the teeth moving forward in four wheel drive, the worn teeth would allow the stub shaft to jump over the teeth in the collar causing the loud bang. The wear was just enough to make it happen with a lot of throttle input, but not under light throttle. The teeth were tapered on the one edge in the direction that it is normally turning, and explains why it would only bang in forward ranges and not in reverse. In reverse it would apply the load to the other side of the teeth that were not worn nearly as bad. Because of the shallow depth of the teeth, once it happened a couple times it got worse fairly quickly.

A couple side notes: this vehicle had been to another shop and had been diagnosed as a jumping chain in the transfer case. I also found out after all was said and done that this customer lived in the country and would leave the truck in auto four wheel drive leaving the front end engaged, and potentially contributing to the wear that was found. Once all the affected parts were replaced, the vehicle performed flawlessly with no noise under load. This was certainly a good learning experience; I can honestly say that I would have bet money that this was a transfer case issue from the beginning. I hope that this information may just help someone with a noise issue on one of these trucks get to the bottom of it quickly.

Real-World Driving Drafted to Dyno-Testing Development

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 is also holds ASE Master and L1 certifications.

One of the cool things I get to do as a part of my job is gather information for our dynamometer testing procedures. We try to gather real-world operating parameters and duplicate this for our dyno tests. Something that I have noticed while doing this is that the solenoid firing order reference charts are not always 100% accurate; the days of a solenoid just either being on or off are pretty much over for us. The focus of this article is the Toyota AB60, as it has a nice balance of five on/off solenoids: S1, S2, S3, S4, and SR. In addition to those, there are 4 PWM solenoids: SL1, SL2, SLT, and SLU which all operate at about 335 Hz. The test vehicle is a 2008 Toyota Tundra equipped with a 5.7L engine.

While the chart for this unit is fairly accurate, there are a couple things that happen in this transmission that are not documented very well. The equipment that we are using is a Yokogawa DL850V Scopecorder which has 10 channels available to use and has the ability to record at an astonishing speed. We also use one or two Pico 500psi pressure transducers depending on the unit or available pressure ports. I won’t go into all the specs of the machine but let’s just say this is not your typical automotive scope.

The screenshots that follow are from the Xviewer software (more of the really cool stuff that I get to play with), also from Yokogawa. The software allows you to view the recorded signals from the vehicle, but not only them, as it also has a “math” function where we can see voltage levels, duty cycles, frequency and amplitude, resulting in about 27 different parameters that we can look at.

Referring to figure 2, the top half is the entire recording, and the bottom half is where you can zoom into any particular section from the top and use the cursor to isolate an even smaller part of the recording. That’s where the math function comes into play; you can put the cursors A and B on any part of the recording, and the software will automatically do the calculations for you. What I have selected here was “Max Voltage”, “Frequency”, and “+ Duty Cycle”.


Figure 2

This is about the only solenoid firing order chart I could find for this particular unit:


Figure 3

Starting with the SL1 solenoid while referencing the chart shown in figure 3, it shows that the SL1 does not turn on until 5th and 6th gears so let’s turn our attention to figure 4, displaying a recording of a 0 to 65mph 1st through 6th gear upshift cycle:


Figure 4

One of the reasons that I chose this unit to use for our example is that it’s really easy to see the shift commands from the simple on/off solenoids, but I also wanted to point out that on the 1-2, 2-3 and 3-4 shifts the SL1 ramps up from 0% to 45% and modulates for about 1.5 seconds before shutting off again. Figure 5 is a zoomed-in screenshot of the first three shifts:


Figure 5

So, from seeing this do you think that SL1 operation could have an effect on any of these shifts? Without knowing this bit of information, if you had a shift-feel issue with any of these shifts, would you even look at the SL1 solenoid? I can tell you that adding simulated operation of this solenoid to the dyno software smoothed the shifts during our tests, and when it was not controlled, the shifts were very quick and bumpy but everything worked and felt fine when the transmission was installed into the vehicle.

The SL2 solenoid is on 1st through 4th gears as shown on the chart, but what the chart does not tell you is that it also turns back on and modulates during the 5-6 shift, just like the SL1 did on the lower ratios. This solenoid also has an effect on shift feel for the 5-6 shift, and a closer view of this operation can be seen in figure 6:


Figure 6

The other strange thing that happens is while the vehicle is stationary in drive the SL2 solenoid is not on while you have your foot on the brake. Huh? Take a look at the beginning of the recording in figure 4, and also figure 7. Simply sitting still in Park, and when I push on the brake pedal, the S4 and SL1 turn on and the SR and SL2 turn off and then reverse when the brake is released.


Figure 7

This is something that we are seeing more and more of where an input, such as a brake switch or a throttle position sensor voltage change, has a direct impact on solenoid operation or even line pressure where the computer (whether it be a TCM or PCM) is anticipating a change in state from the operator. Another example of this is shown in figure 8:


Figure 8

This is a forced 6-5 downshift. As you can see, the SL2 turns on and modulates almost 1 second (the scope view is set at 500ms per division) before the S2 is commanded off to make the 6-5 downshift. You obviously cannot tell this from the screenshot, but the SL2 starts at 35% + Duty Cycle and ramps up to 50% right before the shift, and then tapers off quickly off after. Here are some pressure specs for you: @ idle in PRND 56psi the SLT solenoid operates at 63% + Duty Cycle. Drive-stall 210psi @ 33% + Duty Cycle and Reverse stall 230psi @ 23% + Duty Cycle.

This transmission is just one example, and there are many others that have similar discrepancies in operation. We have scoped and recorded the operation of 33 different units so far, and have many more to go. This process is an integral part of our R&D procedures and new-product development. Dealing with this is just another thing that we as “Transmission Guys” have to be aware of and always try to think outside of the box when it comes to a strange issue. Use all the resources available to you, and if there is anything that does not seem correct or does not seem to make sense to you, get out the scope or meter and start testing.

Solving Dodge Diesel TCC Lockup Issues By Eliminating Connectors

By Mike Greer, Diagnostician

greer-mikeMike has been with Certified Transmission since 1996, and been in the industry since 1987. He is an ASE master Technician and has also served as a Master Builder for the company in the past.

Today’s topic is in regard to the common complaint of intermittent and erratic torque converter clutch cycling between 45MPH-60MPH experienced in Dodge Cummins Diesel pick-ups from years 1998-2003. After 60MPH, the issue seems to go away. This has been a well-documented problem over the years with many bulletins published from the manufacturer.

When the issue first showed itself several years back, it seemed like reprogramming the PCM, cleaning the battery terminals, removing paint from the body ground point, and reconnecting the wiring was the cure. As the years went by, things began getting worse, and also more difficult to correct. One very popular fix was to install a noise filter on the TPS signal wire back to the PCM, as the cause of the TCC cycling problem was a noisy or erratic TPS signal. This is generally common knowledge, and most have seen graphs and screenshots of the erratic TPS signal. What has always bothered me is, why? Why does a truck that has worked fine for years all of a sudden need a noise filter installed to make the transmission work properly, as designed?

My recent experience involved a construction worker’s truck, specifically a 2001 Dodge 2500 Cummins Diesel. A wholesale customer that specializes in diesel engines had been working on this vehicle, attempting to diagnose the cause of the TCC cycling in and out. I started my diagnosis with the usual procedure: connecting the scanner, checking out the fluid, and going for a road test to confirm the problem. Sure enough, the TCC was cycling in and out, so I took a quick screen shot of the scan tool data, and as you can see in Fig. 1, the TCC is actually being commanded by the PCM to go in and out, and the transmission is responding as commanded.


Figure 1

I took the truck back into the shop to check the battery for corrosion and inspect the body grounds; everything was clean, and it appeared that someone had just done exactly what I was going to do. To be sure, I did it again because, up to this point, that fix had been working. Despite my efforts, no dice.

Well (as I scratch my head), what now?

I went to the check-list, and started with a charging system test with the Midtronics ESP-1000 tester (this is the higher-end tester from Midtronics which we have found to be really reliable and accurate). Sure enough, the alternator had excessive ripple of over 750MV. Seeing this, I unbolted the alternator V+ wire, and took the truck out for a drive. It didn’t act up at all. It appeared that the excessive electrical noise from the alternator was causing the issue, so we sold and installed a new alternator, drove it some more, and still had no problems. It was working great. We handed the customer back his keys, and off he went.

This is where that “intermittent” word starts biting me in the “you know what”. Two days later the customer is back with the same problem, and he isn’t a very happy customer at this point. My manager showed him the old print out of the charging system, showing him what we saw, and why he needed an alternator. We took him out to the shop, tested his vehicle again, and compared the two sheets for him to see what we were talking about. He agreed with us there was a problem there with the alternator, but, since it is still happening, there is something else going on there. We told the customer that we were going to need more time with the truck. He said it is his work truck, and without the truck he can’t make money. We agreed that on the next rainy day, he would drop it off with us. A few days later, it was back at the shop for testing.

Back to my check-list.

The system had no codes in it; the PCM was up to date, APP readings were good, throttle linkage working great with no play in it, and the engine was running good. I thought to myself, “Am I going to have to install a noise filter on this truck?” I did not want to, but if I did not find something causing it I might have to.

I reviewed wiring diagrams looking for anything that might stand out, and I noticed that there are two PCM grounds at the main battery ground (figure 2). Two grounds connect at S126 and end up at G115 on the passenger side of the battery cable. As I am looking at the battery, I noticed two connectors on the passenger side rear of the battery. Looking at figure 3, you can see one connector is hiding behind the battery case. Figure 4 shows a close up of the connector.


Figure 2


Figure 3



Figure 4

I proceeded to do a voltage drop test again, and for the third time I really didn’t see anything that raised a red flag regarding poor grounds. Across the two spade connectors referenced in figure 3, there was only a small amount of voltage drop, so I pulled these connectors apart looking for corrosion or anything else that could be wrong. I found no problems there, so I put a little dielectric grease on them and plugged them back in. At this point I was desperate to find the real issue, so I decide to eliminate these connections entirely. We use a hydraulic battery terminal crimper to repair cable ends, so I got a couple of 4-gauge solderless butt connectors and cut the wires on each end of the spade, then crimped them and sealed them with shrink tube.


Figure 5

After completing this, there was virtually no voltage drop. Off for another road test, I have a pretty good feel for this truck by now and have been able to get it in the right situations for the problem to duplicate fairly consistently. This time everything seems to be working as designed, but I wanted to have more time with it to verify the fix 100%, but the owner is up in the office to pick up the truck when I got back, working or not. He drives off and says he will bring it back on another rainy day.

One week goes by, and we don’t see him. A second week goes back and still nothing. So by this point, I’ve kind of forgotten about the truck getting back into our daily work routine. A couple of months later, another Dodge shows up with the same problem. At this point I got to wondering what happened to the other one we had this problem with. I had the manager look up the paper work for that customer, to give him a call and see how that truck is doing. He says it is doing great, and hasn’t had that problem since. Awesome!

With the truck I was now facing with the same problem, I figured I would eliminate these connectors just to see what would happen. Once completed, I rechecked it and the problem was gone.

There is a lot of talk about noise filters, and Identifix has 27-plus fixes using noise filters. What I’d found is that in lieu of installing a noise filter, eliminate these connectors and make sure there is almost no voltage drop in this side of the circuit. If you compare the snapshot shown in figure 6 after the repair, versus before the repair as shown in figure 1, you can see that the TPS voltage is a lot smoother and the TCC problem is gone.


Figure 6

There is one spike on the TCC when it goes into 4th gear, but that is normal and how it is designed to work. Since the first truck that was repaired in this fashion, I have performed this repair on more than 20 trucks and in each case, never seen a comeback.

Transmission Programming Basics

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.

A few months ago I wrote an article about Diesel Tuners in reference to keeping the software updated and some of the issues that can arise if they aren’t. This go around I will touch on something similar but different at the same time: vehicles that have 3rd-party programming installed, but there is no tuner that you can hold onto or plug in and update. This is hardware that has the ability to pull the factory calibration from the ECM/TCM in order to be edited, and then flashed back into the ECM/TCM. HP Tuners and EFI Live are the “big-two” so to speak, and there are a few up-and-comers entering the market but for the most part these are the brands that are the most widely used and can give us some headaches.

I will start out with the disclaimer that I am in no way an expert on the use of this software, but I have been involved with it and even modified a couple of TCM’s for 6L80 units. I figured that I could touch on a few things I have encountered and maybe save someone comeback or even know when to avoid a job if you are not comfortable with it. While there are shops out there that feel confident in tuning vehicles and have the appropriate expertise, there are just as many that THINK they know what they are doing but really don’t. These are the tunes that will wreak havoc in our lives. This software is very powerful. Whether it is HP Tuners or EFI Live, they both accomplish the same thing; it’s just the user interface that differs in appearance. Just to keep it on the simple side, all of the screenshots referenced in this article will be from HP Tuners software.

So, how do you know if a vehicle’s computer has been modified with this software? Good question. The people that program the software are very smart, and this is true also with the handheld tuners. Most will not change the calibration # when you look at it with your scan tool, so this is where the website for GM comes into play. I know that everyone that goes to the yearly technical seminars from ATSG or others has heard of or seen this website. Comparing the CVN # from the website to the one shown on the scan tool is the only way I know to confirm that tuning has taken place, beyond asking the customer. If you suspect programming and the owner does either not want to admit to it, or genuinely does not know, what I have found is that if you tell them that you will be reprogramming the ECM/TCM with the factory software and the vehicle is tuned, it will wipe out the aftermarket tuning. At this point they will either spill the beans, or walk away. Programming isn’t cheap.

The 6L80/90 series units seem to be the most popular GM applications that we see, and the focus of this article. There are so many different parameters in this software that it will be impossible to show you all of them, so I will do my best to show you some examples and you can fill in the blanks from there. In this image I am highlighted on the Auto Shift Speed tab and all of the “buttons” that you see will bring up a table: “Normal” is the 1-2, 2-3 & 3-4 shift tables which will also include the downshifts of the same gears, the 5th & 6th will be the corresponding 4-5 & 5-4 or 5-6 & 6-5.


Figure 1

In the tables below, Full Throttle Shift Speed for Normal, 5th & 6th and you can see that the 2-3 shift at WOT is commanded to happen at 56mph. For an example of how a shift is disabled look at the 5-6 table as it is commanded to happen at 311mph. Since it will never see that mph, the 5-6 will not happen at WOT in a stock calibration. However, this can be changed in the software to whatever speed you want above the 4-5 command:


Figure 2

Now we can move onto Shift time, shown in the next image. This is the transition time from one ratio to another measured in seconds and uses the Turbine speed sensor for reference. As you can see, there are multiple different tables that can be accessed. Some are base tables and others are modifiers, meaning that one table can either modify, or even replace, a base table if certain parameters are met:


Figure 3

In the next image we will look at the Shift Time Torque Adder Upshift-Normal table, this is a “RPM over Torque” table. This will have a direct affect on shift feel, and the lower the number, the quicker or firmer the shift is. So in this example, at 6250 RPM’s and 295 lb-ft of Torque input the commanded shift time is .3994 Seconds. This table can be modified in several different ways; you could change the entire table by a certain percentage or a set amount of time, or even just change individual blocks to whatever you would want. One thing here that can really mess with the transmission is the torque table, or “load factoring” that is generated on the engine side of things; if the load factor is not correct it will have an adverse affect on any table that uses a torque input for calculations, very similar to a skewed MAF sensor. The shift time in these tables (the calculated total shift time that the computer wants to see) is where the shift adapts come into play. If the actual time is greater than what is commanded, the TCM will try to shorten the shift time for that load point. Although the 6 speeds work a little differently, you still can compare this to “Tap Cells” that everyone has seen on the 4L60E or 4T65E:


Figure 4

In figure 5 we see the Shift Pressure tab, and boy, what we could go into here. As defined:

  • Maximum Pressure is the maximum desired line pressure allowed. It is a cap for any shift table value and has the final say on the line pressure offset before it is used on the Force Motor Current table.
  • Maximum Pressure B: Line pressure maximum value, in some cases this value may be calibrated as actual line pressure after the regulator gain has been applied.
  • Maximum Clutch Pressure: Clutch pressure maximum value, in some cases this value may be calibrated as actual line pressure after the regulator gain has been applied.

Figure 5

In figure 6 the Max Line Pressure table is shown, and in figure 7, Base Shift Pressure 1-2 Pattern X: The base line pressure (main line feed pressure solenoid) during a shift:


Figure 6


Figure 7

The next image is the TCC Tab which has control over the TCC Pressure, Slip Speed, Adapts and Apply and release speeds:


Figure 8

I am not going to go into much detail about the TCC Tab because we need to move onto another section that I believe has more of a negative impact on a transmission lifespan, and thus more important to know.

Figure 9 shows the Torque Management tab:


Figure 9

Almost all late model electronically-controlled transmissions have Torque Management built into the software. TM comes into play during the shift transition, as even at stock power levels, the OE limits the torque input to the transmission during shifts. The “Shift Torque Factor” where it shows 1.0 is 100% TM, and that’s what it is set at from GM. This can be changed to anything lower, and in this example I changed the 2-3 to 0.500, which is 50% TM. If you look at Torque Reduction where it shows Enable/Disable, this is where you could completely eliminate TM on any of the parameters listed. Doing so is a critical mistake and has the ability to destroy a transmission, especially on a modified vehicle. It is not uncommon to see a Camaro or Corvette that is either Turbocharged or Supercharged that has 700-1200 HP at the rear wheels, and while it is possible to make a transmission survive in these vehicles, extreme attention to detail has to be used while building the transmission in addition to and modifications to the vehicle’s computer programming.

Advanced Testing via Lab Scope

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 had been fascinated by technology and electronics, and I can remember the first time I used a scope. It was in my high school auto tech class, and we were being introduced to ignition waveforms using a Sun Engine Analyzer. I pulled my 1968 Barracuda up to this huge machine with all kinds of leads coming off of this big arm that hung over the engine bay and everyone in the class was overwhelmed by what was going on. It was amazing to me that my teacher could tell that my points (anyone remember points?) weren’t gapped properly and that I had a bad plug or wire on #3 cylinder simply by looking at the electrical signal on the scope.

Fast forward 40 years. Now we have 4 to 8 channel lab scopes that are built into your scan tool or laptop that are capable of storing and manipulating data at the click of a mouse. We have multiple computer systems controlling every aspect of how our vehicles operate. Just turning on a dome light requires computer requests and verifications from multiple modules. Making a transmission shift is a whole different story. If I’m the PCM or TCM, I have to know if I’m receiving the correct information from other modules, usually on some form of data bus, various sensors, and the list goes on. Same with the airbag module and ABS/Traction control module, and keeping track of what module has control over each function can be a tedious task.

A majority of the time, a lab scope is a good way to verify inputs and outputs to various controllers. Sometimes, it’s the only way. Graphing data on your scanner can reveal many things, but often scan tools are just too slow to pinpoint the problem. Using a lab scope, we can get a complete picture of the electrical signals that the module in question is receiving. Add an amp probe and a pressure transducer to the mix, and we can get a comprehensive look at the signals in real time.

Let’s take a look at a couple of cases that would seem to be simple, but turned out to be a little more involved than expected. This is where experience in diagnosing electrical signals with a scope comes into play.

The first case is a 2004 Ford F550, equipped with a 6.8 L V10 and a 4R100 transmission, with PTO. It came to me with an issue of the O/D light flashing, erratic shifting, and code P0717 (no turbine speed signal). On my initial inspection, the transmission did shift through all 4 gears, although very erratically, and the O/D light started flashing after the first couple of shift commands. I had no turbine speed sensor on the scan data, so I knew I needed to check out the TSS circuit to start with.

I usually use my ohmmeter to check for open or shorted circuits; I really don’t trust it for much else because it doesn’t send enough current through the circuit you’re testing. Voltage drop testing is preferred for finding excessive resistance from bad grounds, poor connections, etc, and you can often find a corroded wire or circuit by doing that. In this case, the sensor tested within range, but then I went to the PCM and checked the resistance between the TSS input terminal and sensor and I found an open circuit. Slam dunk, right? I knew I had a broken wire on the TSS circuit to the PCM. I installed an overlay wire from the PCM to the sensor connector at the transmission, thinking I was good to go, but no – I still had no TSS signal to the PCM.

So, what’s up? According to my ohmmeter, I had a good circuit between the PCM and the sensor. How do I verify that the circuit is capable of sending a signal to the PCM?

Actually, it’s pretty simple: The TSS sensor on this transmission, like many others, is a variable reluctance sensor. Simply put, it’s a coil of wire wound around a magnet, and any movement of a metallic object – tone ring, reluctor (there’s lots of names for them) induces a voltage as the metal crosses the tip of the sensor. It doesn’t have to have any power supplied to it, unlike a hall-effect sensor, to operate.

I took the sensor out of the transmission and hooked up my lab scope to the signal wire at the PCM. I had an assistant take a pocket screwdriver and wave it over the tip of the sensor really fast. I could see that I had a waveform (although erratic as expected) to verify that the sensor and the circuit were both intact. It looks like this:


Figure 1

You can do the same thing with a hall-effect sensor, which usually has 3 wires, power, ground and signal, just turn the key on. But a hall-effect sensor will produce a square wave of some sorts using this method instead of a sine wave.

As it turns out, there was an internal failure of the transmission. The TSS signal is generated by the teeth on the coast clutch drum, and for some reason it was not spinning although the transmission did shift through all 4 gears. Going one step further, I took a mirror and looked through the sensor mounting hole which is easily accessible on this transmission. I had an assistant start the engine and put it in drive and let the wheels spin – sure enough I could see the drum spin for about 2 seconds and then came to a stop. I didn’t tear the unit down to determine the exact cause of the failure, but I knew from the scope data and visual inspection that it was an internal issue.

The next case is very similar: a 2006 Ford Focus that another shop had installed a reman unit into and would turn on the MIL after about a mile or so of driving, and set code P0721 (excessive noise on the output speed sensor circuit). It shifted fine and graphing the OSS showed no glitches or dropouts of the signal. This turned out to be a man-made failure – a self-inflicted gunshot wound, if you will. Here’s a picture of the waveform from the output speed sensor:


Figure 2

Notice the one hump in the waveform that the amplitude is about 1/2 of what it should be where the cursors are? What had happened was that the tone ring for the OSS got slightly bent somewhere during the re-manufacturing process. As you can see by another picture, the tone ring under the side bearing could very easily get one of its teeth bent, and it wouldn’t take much of a bump to bend one enough to disrupt the signal:


Figure 3

I actually tried to measure the depth of the teeth through the mounting hole for the OSS with a caliper – it’s pretty easily accessible – but couldn’t really identify the bent tooth. This puppy couldn’t have been bent more than .015″. I even tried to bend another tooth up to provide a point of reference, thinking if I could find my high tooth, I could count the number of teeth to my low tooth and try to pull it up with a pick. It just didn’t work out; I was trying any means possible to have to avoid R&R the transmission, but no dice.

There are many times, unfortunately, that a simple mistake can lead to a complicated diagnosis. Anyone ever seen a late 90’s Jeep flexplate disrupt the crank sensor signal because someone got in a hurry and bent the window on the flex-plate ever so slightly, but just enough to cause a misfire? Ever had a cylinder head come back from the machine shop with the cam sensor reluctors bolted to the wrong cams? Or one of my favorites, a used car lot swaps a 2.7 L Chrysler motor from the wrong year and the cam sensor signals are entirely incompatible due to design and computer strategy? That all comes from my days in general repair, but it’s things like that that applies to everyday situations and can usually only be found with a lab scope.

So, how do we know what a good scope pattern looks like vs a bad one? Firstly, there may be many good known waveforms already stored on your scan tool or scope. Secondly, there are a lot of known good and bad waveforms on websites or in factory service information. One of my favorites is IATN as that site has a pretty extensive library of waveforms, scan data, and input from thousands of automotive professionals like us. Lastly, use your scope when you get the time to look at a known good waveform, whether it be checking current to an EPC solenoid, or voltage to a shift solenoid for a voltage spike. The more you use it, the easier it becomes to get proficient at diagnosing electrical problems, and everyone profits from it.

Beware of Technical Misinformation

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.

As with most of the accounts we’ve shared detailing vehicle symptoms and repairs, electrical issues seem to be the most common root cause. Our subject today involves a 2003 Dodge Sprinter 2500 that showed up at our door with the customer informing us that they could not shut it off since it would not restart without jumping the solenoid on the starter. The gentleman stated it would not start with the key, the shifter would not come out of park and the transmission would not shift. He also stated that we had installed a TCM approximately a year ago, and since it did not shift the customer thought it was related to what we had done. He also stated he had replaced the fuse in the fuse panel for the transmission and that didn’t help. Apparently, we needed to diagnose some electrical problems.

I began this adventure by scanning the computers for codes. There was a grocery list of codes stored and several communications (U-type) codes including, “No Communication from TCM”. I confirmed that the starter would not crank by cycling the key. I was told it would start by jumping the solenoid, so I knew there was battery power to the starter. Examining the wiring diagram for the starting circuit, I determined that I would need to start by checking the circuit at the starter motor relay.

I observed battery power to the relay pin 87 and pin 86 in the “crank” position. When I cycled the key, however, the ECM was not grounding the relay at pin 85. I replaced the relay with a relay jumper (see fig. 1) so I could easily start the vehicle to test it and move it around. But I needed to find out why the ECM was not providing a ground signal to the relay.


Figure 1

The ECM was located and a quick visual inspection revealed heavy corrosion on one of the connectors. The ECM terminals and the pins in the connector were in poor condition. I thought maybe the connector would need to be replaced. The connector was cleaned and I also cleaned each pin in the ECM until the corrosion was gone. The terminals in the connector were not as bad as originally thought. As I reconnected the ECM I was hopeful that this would fix the vehicle. Unfortunately, that was not the case. The engine still would not crank while cycling the key.

Studying the wiring diagram more closely, I concluded that there must be some input causing the ECM to inhibit the ground to the relay to allow the starter to energize. If I bypassed the ECM and grounded pin 43 (see fig. 2), the vehicle would crank and start. However, the shifter still didn’t work. I needed to figure out what inputs the ECM used to determine whether to inhibit or allow the crank event. I also needed to address the “No Communication” code in the TCM (see fig. 3), hoping that resolving that issue may take care of the other symptoms also.


Figure 2


Figure 3

I double-checked for B+ at fuse #2 (see fig. 4 & 5), which was the one that the customer replaced. It was the only new fuse in the fuse box. I checked the fuse box cover and it confirmed the fuse replaced should be the transmission fuse. Examining the wiring diagram of the transmission power distribution, I could see that the transmission relay powers the TCM and the shifter assembly. A bad TCM relay could certainly cause the customer’s symptoms, so I checked my voltage and grounds at the TCM. I had no B+ at pin 29 (transmission relay output). I located the transmission relay and discovered that no B+ was present at pin 87 (should be hot at all times), but did have B+ at pin 86 with the key in the run position.


Figure 4


Figure 5

Tracing the red wire from the relay box (pin 87 of the transmission relay) to the fuse box under the seat, I found that the wire did not go to the fuse marked “transmission” (fuse #2) as the diagram indicated it should. Instead, it lead to fuse #4, which turned out to be the actual transmission fuse (see fig. 6). There was B+ at the fuse but nothing coming out of the fuse. The fuse “looked” ok. I cleaned the terminals in the fuse box, replaced with a new fuse and everything started working. The engine cranked and started. The shifter interlock was now functioning correctly. After clearing codes and road testing, I confirmed that the transmission itself was now operating correctly as well.


Figure 6

Since the TCM was not powering up, it could not provide the signal required to allow the ECM to enable the starter crank circuit, and in addition, provide voltage to the shifter and transmission.

The most difficult part of this diagnosis was the lack of accurate information. I was misled on several occasions because the manuals were incorrect, and had to back track to figure out what went where. Incorrect wire colors and wrong pin locations make diagnosing difficult. It’s a part of our industry. After studying the diagrams running the test, if you don’t get the results you were looking for, you may have to start at the beginning and work your way through it. Had I tested all of the fuses in the beginning, I likely would have found the issue then. As they say, hindsight is 20/20.

The Case of the Cold TCM

By LJ Porter, Diagnostician

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

A couple months ago we had a customer contact us about a problem that he was having with his 2000 Nissan Frontier 4wd Pickup. While he had some trouble explaining the exact symptoms that were occurring, we understood that the problem only seemed to happen when it was driven first thing in the morning, and that in simple terms, “it just didn’t want to go”. We arranged an appointment for him to drop off the vehicle with us so we could perform our initial diagnosis and evaluation after the vehicle sat outside overnight.

On the initial road test the truck seemed to drive out okay, but there was what I felt to be a slight bind up on the 1-2 shift with all else seeming normal. The next step was to get the truck into a service bay, check fluid, do a battery and charging system analysis, undercar inspection, and scan for codes. The findings of this initial evaluation indicated that the fluid was full but dark, and had a very slight burnt odor. The following codes appeared: P0325 (knock sensor), P0720 (VSS), P0725 (engine speed sensor), and P0732 (gear ratio error 2nd). There were no signs of water or glycol intrusion into the unit. While having an engine side code that related to an engine speed sensor and also the knock sensor code, I felt at this time the best course of action would be to refer him to a general repair shop to complete the engine drivability diagnosis.

The repair facility phoned us after they completed the engine-related repairs and said that there still seemed to be an issue with the transmission, so we went down and picked up the truck for further evaluation. While I could not reproduce the P0732 code, it still had a bind on the 1-2 that kept getting worse the more that I drove it. At this point, I recommended that we install one of our remanufactured transmissions. The manager sold the job and we got the transmission installed, completed the road test procedure, double-checked the complete repair and the truck was delivered to the customer. A few days later the vehicle owner called us and said that the issue had returned and the vehicle was behaving exactly as it had before the transmission was installed. This is the call we all hate to receive.

When he returned the truck for us to inspect, he stated that when he first started it up in the morning the OD light flashed very quickly and the vehicle did not have any power. The next morning was really cold and ideal for duplicating the customer’s concern. When I started the truck, I verified the customer’s concern as the OD light was blinking rapidly and the transmission was in failsafe. I noticed that the OD light seemed to be abnormally dim, but by the time I got the truck into the bay and hooked up the scan tool the OD light had stopped blinking. I scanned for codes and found none, and truck was no longer in fail-safe mode and seemed to drive normally at that point. So what changed? I did not move anything and didn’t even open the hood, so how did it fix itself? This was puzzling.

Once again I left the truck outside in the cold for several hours until the problem reoccurred, and when I hooked up the scanner I discovered that the scan tool had no communication with the TCM (Figure 1). Communication was okay with the ECM and ABS modules, but not the TCM. I proceeded to check the power and grounds to the TCM, and all connections and wiring seemed to be in order. By the time I got done with these checks, I realized that the TCM was communicating again with no codes stored.


Figure 1

The only solid lead that I had was that I could always reproduce the issue when the vehicle was cold, and the TCM had no communication which seemed to be at the heart of the problem. Focusing on the TCM itself, I removed the module from the truck and placed it into the freezer, leaving the truck inside our warm shop. After a couple of hours, I retrieved the TCM from the freezer and reinstalled it into the truck, and voilà! The OD light was dimly blinking and the TCM had no communication with the scan tool.

To speed up the process and test the theory, I grabbed my heat gun and started warming up the TCM (Figure 2) and fairly quickly regained communication with the TCM.


Figure 2

It also had a P1605 code in the ECM (Figure 3). I repeated this testing sequence again just to make certain that this was indeed the problem, and sure enough, got the exact same results.


Figure 3

A new TCM for this vehicle is a 2000 model year-only application and was priced at more than $500.00. Since I had never replaced a TCM for this application and none of our other 14 locations had either, I figured that a used TCM would be a fairly safe bet and picked one up at a local salvage yard for $75.00. I installed the used part and everything worked as it should. Just to be on the safe side, I took the used TCM and dropped that in the freezer also and it worked even when frozen. We returned the truck to the happy customer a couple of months ago, and the vehicle owner reports that all is well.

In the end, the experience was a very unusual one. The decision to replace the transmission was in part due to the fluid condition, but the root of the problem came down to intermittent TCM operation caused by cold temperature conditions. The key to solving these types of issues is to remain persistent and find the common links to the problem. If you can isolate the clues to a handful of repeatable conditions, it won’t be long before you solve the problem and win the customer.