Lack of sleep, anxiety, dread going to work? Everyone that works in this business has had that feeling at one time or another. Sometimes you wish you had received a few sticks of dynamite for Christmas to help you eliminate those pesky transmission problems that refuse to go away.
This issue is one of those problems that most would not want to see come through their door. GM applications equipped with a TEHCM (Transmission Electrical Hydraulic Control Module) such as the 6L and 6T equipped vehicles can exhibit any of the following concerns in any combination:
- MIL on
- Only one DTC set or any of the following DTCs may be set in any combination. DTCs P0562 Low voltage, P0742 TCC stuck on, P0776 Solenoid 2 stuck off, P0796 Solenoid 3 stuck off, P0965 Solenoid 2 performance, P0969 Solenoid 3 performance, P2714 Solenoid 3 stuck off, P2715 Solenoid 3 stuck on, P2719 Solenoid 3 performance and/or P2762 TCC solenoid performance.
- No DTCs set
- No forward
- No reverse
- No forward or reverse
- Ties up going forward
- Ties up going in reverse
- Hard shifts
- Stalling
- Hesitation during acceleration
- Default actions such as reverse/3rd gear only
- Default actions such as 2nd gear only
- Default actions such as 2nd and 4th gear only
Any of the issues can occur independently or in combination with other problems. And like many issues we deal with today, the symptoms are likely to be intermittent in nature and temperature-sensitive. As a result, you may have specific symptoms one day and different symptoms the next day.
At this point, you are probably wondering what all the different symptoms and transmission applications have in common. In simple terms, the 6L50, 6L80, 6L90, 6T70, 6T75, 6T80 all use the same design TEHCM. Let me explain before you get upset and rip this page out of the magazine. The TEHCMs for all applications use different part numbers, which means they may not be interchanged with another part number, but all of the TEHCMs are manufactured by Bosch for GM. In addition, all TEHCMs use the same microprocessor, so they are the same design even though their interchange is limited.
This also means if you have an issue with a TEHCM and it is microprocessor related, it is likely to affect not only 6L45 (MYA), 6L50 (MYB), 6L80 (MYC), 6L90 (MYD) applications but also 6T70 (M7U, M7W) applications as well. So here is how you will see the scenarios we just discussed play out. It could be a Tahoe, Acadia, Canyon, Sierra, Yukon, Silverado, Colorado, XTS, Express, Impala, or Suburban. The cause and the repair will be the same across all the vehicle lines and models.
Bosch had an issue with a capacitor internal to the TEHCM that could cause a problem with microprocessor operation when the capacitor was acting up. So, any time the capacitor was having a “bad day,” it could have some form of dramatic impact on the operation of the TEHCM. But, on the other hand, if the capacitor was having a “good day,” all was well in transmission land.
Issues precisely like this make it so difficult for shops today. If you are fortunate enough to be working on the vehicle when it is acting up, you have a good chance of diagnosing and repairing the concerns. However, if the customer states that the transmission was acting up last week, but this week all is well, that becomes a lot more difficult to resolve.
GM and Bosch have identified build dates when this issue may most commonly occur. The model year 2018 with TEHCM build date 7209 (July 28, 2017) through build date 7262 (September 19, 2017) has known issues with the capacitors. This means any TEHCMs built between those dates are likely to fail at some point. If you are working on a unit that falls between those dates, I would suggest that you plan on replacing the TEHCM even if the unit is not acting up as it may develop problems down the road. Comebacks are tough on all shops, and this is one that it is best to get out in front of as the odds are not in your favor. Even if your build date falls slightly outside the known build date issues, I have seen transmissions that exhibit some of the concerns listed above that were repaired by replacing the TEHCM.
To identify the build date, examine the numbers inked onto the TEHCM. Just below the QR code on the TEHCM, you will find a 13-digit number (Figure 1). Reading the number from left to right, inspect positions 5-8, as those numbers represent the build date for the TEHCM.
Diagnosing transmission issues is a challenge even for the best in the industry, and it gets even more challenging when it is an issue like we are discussing here. Customers do not understand how tough it is to diagnose many of the concerns that come into your shop daily. Sure, if you have seen the issue a dozen times, you can tell the customer precisely what it is, but if it is the first time you have seen the issue or if the problem is intermittent, it gets a lot tougher to identify the cause positively. That is why it is critical that you keep yourself and your shop as up-to-date as possible, so I look forward to seeing you at an ATRA seminar this year.
Until next time remember, “Don’t let yesterday take up too much of today.”
