11' Denali - DOD survivor, but now transmission shot?!?!

[2011DenaliInKY]

I can't believe nobody here is familiar with this. 6l80e failure is extremely common after arm/dod lifter failure. A lot of people don't associate the two as being related because very few people know how a 6l80e works or even that it works in a completely different manner than conventional automatic transmissions. When the engine has a dead cylinder for any reason actually, the strategies used to apply torque management are working off data that it doesn't know how to process. The operation of a 6l80e is based around torque management. It uses this data much more than any other transmission and if a truck is driven with a failed lifter for more than just getting it home, it will smoke a 6l80e. If you've done it and gotten away with it, there's a good chance that you've compromised the transmission and just don't know it..

I know it was less than 10 miles once the lifter failed, and it failed all at once, no warnings or sounds catching my attention prior to the incident. I didn’t drive it at all, only started it a few times while diagnosing the problem. I’m trying to learn all I can about how these engines and transmissions operate, I went into the diesel side, power generation in particular, and haven’t worked cars/trucks in years. Any more insight is greatly appreciated!

 

[ivin74]

I know it was less than 10 miles once the lifter failed, and it failed all at once, no warnings or sounds catching my attention prior to the incident. I didn’t drive it at all, only started it a few times while diagnosing the problem. I’m trying to learn all I can about how these engines and transmissions operate, I went into the diesel side, power generation in particular, and haven’t worked cars/trucks in years. Any more insight is greatly appreciated!

Have you checked for codes yet? At this point I would have taken it to a transformation specialist to have them look at it. It would keep you from throwing parts at it.

 

[2011DenaliInKY]

Have you checked for codes yet? At this point I would have taken it to a transformation specialist to have them look at it. It would keep you from throwing parts at it.

It isn’t throwing any codes, none that show on a generic OBD-II scanner or on the dash anyway. I’ve taken it to a couple local shops and everyone sees that it has some mileage on it and says it’s time for a transmission rebuild/replacement. I just don’t buy that with the evidence I’ve found this far. No metal in the pan, good clean fluid, valve body check balls all in good shape and where they’re supposed to be. I feel like it almost has to be something related to the ECM “tuning” I had done, but I don’t have any proof, and have yet to find anyone that’s willing to dive into it and truly troubleshoot and diagnose the issue based on the history of the failure. I’m curious as hell, but also need my ride back on the road again, and don’t want to drop $3-4K for a transmission if I don’t really need to. It’s just frustrating as hell… and doesn’t make any sense to me. I do appreciate all of the insights and welcome anymore that anyone can provide!

 

[ivin74]

It isn’t throwing any codes, none that show on a generic OBD-II scanner or on the dash anyway. I’ve taken it to a couple local shops and everyone sees that it has some mileage on it and says it’s time for a transmission rebuild/replacement. I just don’t buy that with the evidence I’ve found this far. No metal in the pan, good clean fluid, valve body check balls all in good shape and where they’re supposed to be. I feel like it almost has to be something related to the ECM “tuning” I had done, but I don’t have any proof, and have yet to find anyone that’s willing to dive into it and truly troubleshoot and diagnose the issue based on the history of the failure. I’m curious as hell, but also need my ride back on the road again, and don’t want to drop $3-4K for a transmission if I don’t really need to. It’s just frustrating as hell… and doesn’t make any sense to me. I do appreciate all of the insights and welcome anymore that anyone can provide!

Several years ago my BMW 's transmision started acting up. No codes were present so I took it to a transmision shop and they wanted to sell me a transmision. I then to it to BMW and the told me the valve body was bad and they wanted to sell me a new valve body for $5k. I saw several videos YT, I removed the valve body shipped it to a rebuilder and had it back it a wk. $500 bucks later I was on the road again. The point here is to have several folks look into it before they take ur money, you can't trust the mechanic shops now these days.


Go to the https://www.performancetrucks.net/forums/ and ask those guys. Those folks have alot of knowledge with the 6l80s

 

[Geotrash]

It isn’t throwing any codes, none that show on a generic OBD-II scanner or on the dash anyway. I’ve taken it to a couple local shops and everyone sees that it has some mileage on it and says it’s time for a transmission rebuild/replacement. I just don’t buy that with the evidence I’ve found this far. No metal in the pan, good clean fluid, valve body check balls all in good shape and where they’re supposed to be. I feel like it almost has to be something related to the ECM “tuning” I had done, but I don’t have any proof, and have yet to find anyone that’s willing to dive into it and truly troubleshoot and diagnose the issue based on the history of the failure. I’m curious as hell, but also need my ride back on the road again, and don’t want to drop $3-4K for a transmission if I don’t really need to. It’s just frustrating as hell… and doesn’t make any sense to me. I do appreciate all of the insights and welcome anymore that anyone can provide!

A generic scanner can’t read the TCM. You need a Tech2 or equivalent. And, as @swathdiver said, you can also use it to run the transmission relearn procedure, check line pressures, solenoid operation, all kinds of useful diagnostic stuff. Without that, you might as well be using gazing stones.

If it can’t be solved electronically, then the transmission has to come out and be torn down because the cause is mechanical.

I used to have a ‘98 BMW 740iL that one morning would barely move in first gear or reverse, but all other gears were fine. Bought a quality scanner that could read everything on the car and pulled a bunch of conflicting codes from the TCM including ones showing an unexpected difference between input and output shaft rotation. Pulled the transmission out (ZF 5HP24), put it on my workbench and tore it down. Turned out to be a failed 1st gear clutch drum. The pressure regulator in the valvebody on those units would start wearing out and slam the 1st gear clutch piston into the snap ring and eventually bust it through its groove. No visible signs in the valvebody at all, but it was obvious when I got the rest of the thing torn apart. I replaced the drum with a stronger redesigned part, and I replaced the pressure regulator piston as well with a revised one from transgo to keep ot from happening again. Transmission was still working great when I sold the car a few years later.

But that’s the process. Start with the electronics and use the right tool for the job. If that doesn’t work and you have the time and skills, pull it out and see what’s going on. Or, pays yer money and takes yer chances with a shop.

 

[Apach 031]

I know it's not completely the same, but I had a 2017 Sierra with almost identical issues. It was only a year old at the time, and about 25000 miles. The infamous 8l90e. Luckily, I had the extended warranty. Took the dealer 2 weeks to figure out it was a 12 dollar part (mode selector sensor/switch I think) that had failed. Had to scan it, and get the engineers at gm to look at the data. Trans didn't understand what gear I was selecting, and when it found itself moving, had an absolute meltdown. Traction control would apply the brakes, it would shift down and redline randomly, slip like crazy in every gear until it reaches cruising speed, and threw every warning light and message it had. Stranded me on the highway 2 hours from town. I traded it in shortly thereafter, because I was pretty sure it took years of life out of that transmission.

So, yes, my 2 cents is it's something electronic, and you probably want a tech 2 to continue your investigation.

 

[2011DenaliInKY]

I know it's not completely the same, but I had a 2017 Sierra with almost identical issues. It was only a year old at the time, and about 25000 miles. The infamous 8l90e. Luckily, I had the extended warranty. Took the dealer 2 weeks to figure out it was a 12 dollar part (mode selector sensor/switch I think) that had failed. Had to scan it, and get the engineers at gm to look at the data. Trans didn't understand what gear I was selecting, and when it found itself moving, had an absolute meltdown. Traction control would apply the brakes, it would shift down and redline randomly, slip like crazy in every gear until it reaches cruising speed, and threw every warning light and message it had. Stranded me on the highway 2 hours from town. I traded it in shortly thereafter, because I was pretty sure it took years of life out of that transmission.

So, yes, my 2 cents is it's something electronic, and you probably want a tech 2 to continue your investigation.

I really appreciate you sharing your experience, sounds like a rough ordeal! I guess I’m glad I’m not the only one. I need to find a good diagnostic guy to help me out I believe. Thanks and have aMerry Christmas!

 

[swathdiver]

I really appreciate you sharing your experience, sounds like a rough ordeal! I guess I’m glad I’m not the only one. I need to find a good diagnostic guy to help me out I believe. Thanks and have aMerry Christmas!

You are your best diagnostic guy, get a Tech-2 and the shop manual.

 

[ivin74]

I really appreciate you sharing your experience, sounds like a rough ordeal! I guess I’m glad I’m not the only one. I need to find a good diagnostic guy to help me out I believe. Thanks and have aMerry Christmas!

There is a tread on this forum that tells you who has a Tech-2 and their location. You might get lucky and one of those guys might be close to you.

 

[2011DenaliInKY]

You are your best diagnostic guy, get a Tech-2 and the shop manual.

Touché… I’m looking at the Tech2 now. Have any advice on a reputable site to purchase from? I see some knockoffs available, but don’t know which ones are good and which to avoid.