P0796 Code 2015 Sierra and Tranny is Toast?

Brit717 · October 25, 2019

2015 Gmc Sierra, 106K miles

I have searched and I am not getting much luck with this code (P0796) for this type of vehicle. Last weekend, the truck started acting like it had a misfiring cylinder. It was hesitating on acceleration at highway speeds, sputtering a bit, nothing serious but noticeable. No CEL.

We thought maybe bad gas or spark plugs as the truck has over 100K on it and we haven't changed them yet. It is on our list to do anyways for the 100K tune up. We put some gas additive in and it semi resolved itself, not happening as often or as bad, with plans to do the sparks and visual inspection of the coil packs and wires this weekend.

Yesterday afternoon, driving to the gas station, I go to accelerate after the turn and the RPM shoot through the roof, like the truck is in neutral. I pull over, cant get the truck to work properly. Shut it off and wait about 5-10 min, start up again and it finally works and I'm able to finish pulling into the gas station. At this point the CEL does come on and its the P0796 code. Bring it straight to my mechanic and he states that the Tranny is toast. The fluid level was fine, but the fluid was more of a brownish red instead of the redish-orange. He explained that inside of the transmission, something basically deteriorated and caused a whole bunch of damage inside.

He is quoting me $3700 for complete install of a crate transmission with a 3yr warranty on it. Dealership we bought the truck from is quoting $5500.

So I guess, has anyone else had this issue? Is there any TSB or recalls for this issue, and if not, what could be my best course of action? I feel like just over 100k miles is really early for a transmission to break down so quickly. Thanks!

Snowcamo · October 25, 2019

It really varies. Id shop around as I've gotten a solid $2500 with install and upgrades from a few local shops. I'll never put a factor part back in this truck once things start to brake. Just doesnt make sense.

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Ozer · October 25, 2019

Very similar situation to what happened to me..

I was chasing a misfire, replaced everything and still was doing it, under light load. Sputter and skip/clunk..

Long story short, all that driving around was causing more and more damage. My torque converter was going out. When i brought it the GM dealer they were amazed i drove it in there.

They found chunks for metal in the pan. TC has shattered basically. Tranny was toast, same thing $5500 out the door with another crappy GM transmission.

I got it towed out to a local tranny shop that i had mutual friends with and was able to get a full rebuilt with upgrades and mods for $2700 cash.

Dont pay to have another GM one put in UNLESS... you fight it with GM and win. 6k over the warranty is close enough that they may cover it fully.

In past experiences i used social media like FB to reach out and make a complain. This worked with BMW but didnt work with GM, but i didnt follow thru with GM since i was 25k over the warranty.

This is a known issue with the TC going bad, they replace lots of them at dealer. Dont give up and get it covered under good will warranty if you can.

Here is my post from earlier..

Edited October 25, 2019 by Ozer

1SLOW1500 · October 27, 2019

Yes trans issues. Best way to get a good life cycle out of they is regular trans fluid change and reset adaptive tables after that.
On the 6l80e find a local good used trans with super low miles and swap it. Labor is 700-1000 2wd or 4wd. So net a killer deal and be under 2k, core on a trans is $$$.
Make sure your converter is good or you will burn another trans. The tune is set for lots of slip and is one of the issues other is the stock converter. Gm did have issues with them and replaced them.

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Brit717 · October 28, 2019

So I have a case into GM to hopefully get some/most of it covered. We originally brought it to a transmission place but as we are hoping to have GM cover a portion of it, towed it to a GM certified dealer. They looked at it this morning, metal shavings in the fluid and tech says that it smelled "burnt up". The dealer quoted $4500 to do it but we are waiting to see if they come back at us with something from GM.

What really grinds my gears is that apparently the tech stated that this is caused by mileage. We have babied this truck. Most of the mileage is highway, always up on our oil changes and tire rotations, always doing maintenance as required. We have only towed light loads and never been off roading. For the transmission to fail so quickly with no warning.... with only 107k miles on it, no way!

flyingfool · October 28, 2019

On 10/27/2019 at 9:27 AM, 1SLOW1500 said:

Yes trans issues. Best way to get a good life cycle out of they is regular trans fluid change and reset adaptive tables after that.
On the 6l80e find a local good used trans with super low miles and swap it. Labor is 700-1000 2wd or 4wd. So net a killer deal and be under 2k, core on a trans is $$$.
Make sure your converter is good or you will burn another trans. The tune is set for lots of slip and is one of the issues other is the stock converter. Gm did have issues with them and replaced them.

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will a tech 2 clone or HPTuners reset the adaptive tables in the TCU?

1SLOW1500 · October 28, 2019

will a tech 2 clone or HPTuners reset the adaptive tables in the TCU?

Yes you can request it or it also does it automatically when the trans is flashed. And that is important because how would you know your settings are being ablied or it is still in where even the tcm left it at. Then we data log the trans so we can see it our tune is any good or if the adaptive tables are moving it too much. And what slips and speeds. Then we keep tuning trans till the adaptive doesn't change much, slip is reasonable to low and enjoy.

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flyingfool · October 29, 2019

can the tech 2 also program key fobs for GM cars and trucks?

what about the ABS and airbags, what other tricks can it do in the body computer?

1SLOW1500 · October 29, 2019

can the tech 2 also program key fobs for GM cars and trucks?
what about the ABS and airbags, what other tricks can it do in the body computer?

It need different cards to allow it to do some features. Much like the vin swap in the pcm. For obvious reasons they try to limit how has access to that. I am not up on all the feature and what they now offer.
Sounds like you would rather look into open source software. Guys with the Denali clusters have this. If you scroll to the end screen it says open source and a web site.
The hpt is the best scanner for data. And has access to all tune and pcm stuff.
Only thing I here most people want is longer remote start run time.

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flyingfool · October 29, 2019

but there are no accessory cards used in the clone tech2 ?

DaveS314 · December 12, 2021

On 10/28/2019 at 9:00 AM, Brit717 said:

So I have a case into GM to hopefully get some/most of it covered. We originally brought it to a transmission place but as we are hoping to have GM cover a portion of it, towed it to a GM certified dealer. They looked at it this morning, metal shavings in the fluid and tech says that it smelled "burnt up". The dealer quoted $4500 to do it but we are waiting to see if they come back at us with something from GM.

What really grinds my gears is that apparently the tech stated that this is caused by mileage. We have babied this truck. Most of the mileage is highway, always up on our oil changes and tire rotations, always doing maintenance as required. We have only towed light loads and never been off roading. For the transmission to fail so quickly with no warning.... with only 107k miles on it, no way!

I know this post is a couple years old, but I just had this EXACT thing happen. 108k miles. Wondering what your outcome with GM was.