08 Denali XL shifting problems

[Dino615]

Hey all. I am having issues with my trans not shifting from gear to gear. If I just accelerate normally it does ok but if I have to get on it at all like merging into traffic it will actually completely miss the shift and got into a neutral state. The RPMs will continue to climb based on my accelerator but the engine is just revving up and it's not actually in a gear. It will also sometimes get stuck in a gear where it's revved up very high and when i let off the accelerator it will then upshift to the proper gear. Today I tried doing all the shifting manually and it was find if I do it manually but it is having a hard time in automatic shifting, especially on hard acceleration.

I am not getting any engine codes for any trans issues.

THank you.

 

[Tonyrodz]

Start with the simple first--how's your trans fluid? Burned? Level good? Notice any smells?

 

[swathdiver]

Do you have an advanced scan tool like the Tech2? I would imagine that there are internal codes. There's another fellow on here having similar problems right now. Solenoids are getting stuck and there are things to do to attempt to clean them and reset them before replacing the whole TCM.

 

[Dino615]

Start with the simple first--how's your trans fluid? Burned? Level good? Notice any smells?

I did check the fluid levels. Actually right in range and look normal. No discoloration or smell at all.

 

[Dino615]

Do you have an advanced scan tool like the Tech2? I would imagine that there are internal codes. There's another fellow on here having similar problems right now. Solenoids are getting stuck and there are things to do to attempt to clean them and reset them before replacing the whole TCM.

I have a scan tool but I don't know if it's advanced. It's an Innova 3100J. I got it because my last car was throwing airbag codes and this does SRS and ABS. This was the same price as a scan at the dealership and more convenient. It has not picked up any codes recently. About a year ago it threw a couple of codes but they went away. PO989-00 Transmission Fluid Pressure Switch 5 CircuitLow Voltage and PO872-00 Transmission Fluid Pressure Switch3 circuit Low Voltage.

It has not thrown any codes since so with environmental conditions and car washes I figured that was a temporary error.