2015 Yukon Denali 6.2 trans problem

zmnypit · March 3, 2021

Anyone experienced the delay in Reverse on the 8spd trans? Happens after sitting for an hr or so like its losing pressure has has to build back up. You can get in, start it, then put in reverse and the engine will just rev for 3-5 secs before moving. Its been in and out of 2 dealerships for over 2yrs now with the same issue. Finally called GM customer care and got the ball moving on trying to get this resolved. Dealerships say they cant replicate it or they had to reprogram the TCM/ECM which does absolutely nothing.

mookdoc6 · March 3, 2021

We got clunker, shakers and delayed engagers! Step right up...come on down! We gots dem dare finest trucks in town!

lucas287 · March 3, 2021

If you're unfamiliar with HP Tuners this will look a little complex to you. Here is the base pressure for reverse compared to 1st gear. As you can see it calls for ~ 8 times the pressure of 1st gear, which has the highest psi of any forward gear.

With that said, I haven't experienced this issue with my 8 speed. Sorry that no one can figure it out either! Sometimes mine is pretty laggy and then it clunks but never that long of a delay. I'm going to experiment by greatly reducing the first two columns to see what happens and report back. If it engages quicker and with less force, then I'd consider it a win.

lucas287 · March 3, 2021

CamGTP · March 3, 2021

Lucas, you have one table in PSI and the other in KPA. So what you say is not as true.

If you switch to PSI for both tables they are nearly the same.

Edited March 3, 2021 by CamGTP

lucas287 · March 3, 2021

1 hour ago, CamGTP said:

Lucas, you have one table in PSI and the other in KPA. So what you say is not as true.

If you switch to PSI for both tables they are nearly the same.

Crud! Good catch man. Considering I've never touched the reverse table that makes sense. I've played with 1-8 quite a bit and never liked KPA so I switched all of those tables over.

In any event I cut the values in half for the first two columns as a test and it feels no different. So therefore I dont think there's anything from a tuning perspective that can be done to help. But i have had the dealer flash "the latest calibration" before and then downloaded it into HPtuners and compared to before and haven't spotted any differences. So maybe their updates change something I dont have access to??

zmnypit · March 4, 2021

19 hours ago, lucas287 said:

If you're unfamiliar with HP Tuners this will look a little complex to you. Here is the base pressure for reverse compared to 1st gear. As you can see it calls for ~ 8 times the pressure of 1st gear, which has the highest psi of any forward gear.

With that said, I haven't experienced this issue with my 8 speed. Sorry that no one can figure it out either! Sometimes mine is pretty laggy and then it clunks but never that long of a delay. I'm going to experiment by greatly reducing the first two columns to see what happens and report back. If it engages quicker and with less force, then I'd consider it a win.

I am. Spent hrs and hrs tuning LS cars back in the mid-late 2000s. Unfortunately my car was broken into and my laptop/cables stolen. I reached out to HPtuners about replacements but they wanted me to buy all my licenses again as well as new cables etc so I opted out. Anyways, its at the dealership right now. They called this morning and stating they have an open case with GM technical assistance on how to proceed that it defiantly wasn't normal. Will update once I find out more.

mookdoc6 · March 4, 2021

3 hours ago, zmnypit said:

I am. Spent hrs and hrs tuning LS cars back in the mid-late 2000s. Unfortunately my car was broken into and my laptop/cables stolen. I reached out to HPtuners about replacements but they wanted me to buy all my licenses again as well as new cables etc so I opted out. Anyways, its at the dealership right now. They called this morning and stating they have an open case with GM technical assistance on how to proceed that it defiantly wasn't normal. Will update once I find out more.

Delayed engagement 8L90 has 3 seconds before GM deems out of spec? Lol...sounds like a relearn probably to fix yours

zmnypit · March 5, 2021

On 3/4/2021 at 12:38 PM, mookdoc6 said:

Delayed engagement 8L90 has 3 seconds before GM deems out of spec? Lol...sounds like a relearn probably to fix yours

3 sec is being on the low side. Its had about 4 relearns already. Just last week it had Fast Adapt Learn with SPS performed clutch learn with GDS according to the receipt I got. Did not fix it. Made it home from the dealership, parked in the driveway then left 45min later to pickup my daughter and delay was there. Doesnt seem to only happen after sitting overnight.

mookdoc6 · March 5, 2021

13 minutes ago, zmnypit said:

3 sec is being on the low side. Its had about 4 relearns already. Just last week it had Fast Adapt Learn with SPS performed clutch learn with GDS according to the receipt I got. Did not fix it. Made it home from the dealership, parked in the driveway then left 45min later to pickup my daughter and delay was there. Doesnt seem to only happen after sitting overnight.

Ok, sounds like it's time for new valve body?