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.

 

[Campie]

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.

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.

Can you elaborate on those things to do to attempt cleaning? We are getting just the one code PO989-00 which is low voltage on

 

[Campie]

Sorry, low voltage on switch 5.

 

[swathdiver]

Can you elaborate on those things to do to attempt cleaning? We are getting just the one code PO989-00 which is low voltage on

I don't remember specifically, that was a long time ago for my brain!

I might have been referring to the Service Learn Adapts function. Clean fluids ought to clear up the problem. If not, the TECHM or valve body could be rebuilt on your kitchen table and the transmission does not have to come out. Those parts are accessed through the pan.

Brain fog is clearing... I think we summoned Nick's expertise in another thread, didn't we? He's forgotten more than I know about transmissions.

 

[donjetman]

@Campie
Here's a thread I did w/pics and video links to cure my tranny woes:
https://www.tahoeyukonforum.com/thr...p0842-p0872-p0877-update.145047/#post-1838408

 

[Campie]

@Campie
Here's a thread I did w/pics and video links to cure my tranny woes:
https://www.tahoeyukonforum.com/thr...p0842-p0872-p0877-update.145047/#post-1838408

Yikes… That looks like a lot of work! I will watch the videos! We don’t have any problem shifting, driving or towing. It’s just that one code. I’m not knowledgeable enough to know whether the code is a constant or occasional. It’s at the shop now and they are going to investigate the transmission fluid. Drop the pan changed the filter and the fluid 11,000 miles ago, but I don’t know when or if there was a code before that because I didn’t have a scanner then. Lots of fun stuff!