TCM/transmission

[Pfrantz]

Just purchased an 2009 Tahoe from a friend that replaced the transmission.(6L80). At slow acceleration the transmission shifts decently smooth. If I accelerate much more aggressive it over revs before shifting into the next gear. It downshift smooth,this just happens on up shifts. Lightly researched and the most common thing that comes up is the TCM could be going bad. Does this sound like a bad TCM? Is there a relearn process I can do on the TCM?

 

[swathdiver]

Just purchased an 2009 Tahoe from a friend that replaced the transmission.(6L80). At slow acceleration the transmission shifts decently smooth. If I accelerate much more aggressive it over revs before shifting into the next gear. It downshift smooth,this just happens on up shifts. Lightly researched and the most common thing that comes up is the TCM could be going bad. Does this sound like a bad TCM? Is there a relearn process I can do on the TCM?

Hi, @AirJordan613 is experiencing something similar or the same thing with his 2009 Tahoe right now. He's having a shop diagnose it right now.

On Saturday night, my daughter's Sierra started revving up once it got into 4th gear and above. A few minutes later it threw a P0796 and went into reduced power mode. After we got the truck home, the fluid is burnt and black and the fluid was changed about 20K miles ago by the previous owner.

It is possible that a Service Learn Adapts may help the transmission to relearn but that is really only to be used after a repair or replacement or a tune.

 

[Joseph Garcia]

You could reprogram the TCM (reinstall the OEM base program in the TCM), to be ensure that the TCM is not the source of your issue.

 

[Pfrantz]

At the moment I am still trouble shooting the over revving issue. I’ve taken it to a few different shops and a common thing is they say it needs to be tuned properly. The transmission came off of a suburban but was never flashed. The mechanic said it shifts fine but the shift points need to be adjusted. The last shop said he has a friend that has HP Tuners and will check with him. I will update when I receive more information.

 

[swathdiver]

At the moment I am still trouble shooting the over revving issue. I’ve taken it to a few different shops and a common thing is they say it needs to be tuned properly. The transmission came off of a suburban but was never flashed. The mechanic said it shifts fine but the shift points need to be adjusted. The last shop said he has a friend that has HP Tuners and will check with him. I will update when I receive more information.

So this is a used transmission out of a Suburban? At the very least, the Service Learn Adapts should have been performed. A Tech-2 or similar tool can do this, no need for a tune yet. Then drive it and it will begin to relearn.

 

[Geotrash]

So this is a used transmission out of a Suburban? At the very least, the Service Learn Adapts should have been performed. A Tech-2 or similar tool can do this, no need for a tune yet. Then drive it and it will begin to relearn.

^^^ This.

 

[Pfrantz]

UPDATE: dropped off at dealer today for the TCM to be flashed. I will find out this afternoon if this corrected the issue. I noticed also that I had a hard time starting the Tahoe after it was cold. I hooked up my scanner an noticed I was getting negative long term fuel trim and the alcohol % was reading 60. This is a flex fuel Tahoe but I have not used E85. So since I had it at the dealer I had them also reset alcohol content and clear fuel trim tables. But I will know for sure this afternoon if this resolved the issue.