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

[2011DenaliInKY]

Howdy Everyone!

This is my first post here, glad to see a group of people sharing knowledge! I've got a 2011 GMC Yukon Denali with the 6.2L and 6L80 transmission. I recently suffered a collapsed intake lifter on the #1 cylinder, but was able to get it freed up using a special tool I learned about from Crazed Performance Repair (check out Charles on YouTube if you've not already) and sent the ECM out to LT1Swap.com to have it tuned to turn the DOD/AFM system off. While waiting for the ECM to return, I changed the plugs and wires and buttoned up the intake and everything else I had apart while freeing up the lifter. So on Monday my ECM arrived back to me, I was tickled to death to get my truck back on the road. I had the battery disconnected the entire time the unit was down, and swapped it out for a new one as well. So I plugged the ECM in, connected my battery, triple-checked all the wiring connections, and fired it up. The engine ran great, smooth idle, no immediate lights on the dash, no lifter ticking or engine misfiring, I'm in business!! So I thought... I pulled out of the driveway and started getting all the typical warnings on the dash "service stabilitrak", "service traction control", "service side blind zone alert system" and a check engine light. When I went to pull out onto the road it just didn't feel right, the engine was smooth, but it was like my transmission was slipping, bad! I noticed that the little indicator on the dash to let you know which gear you're in didn't move with the gear selector. I also noticed the trans temp was not being displayed like it usually did. I made a short trip, maybe half a mile, and came back home, livid! I slept on it Monday night and all day at work on Tuesday I kept thinking what I could've missed. I thought it had to be some communication issue between the TCM and ECM. I emailed the tuner, he claimed it was nothing he could've done. I got home yesterday and looked EVERYthing over again. I pulled open the main fuse panel under the hood and started reading some circuit names and came across a 15 amp fuse for "TCM batt" (I think that was the name, I forgot to snap a pic of it) that was missing a fuse. For the sake of trying it, I put a 15 amp fuse in that spot, then fired it up again. I noticed that I didn't get any of the warnings now, the trans temp was displayed, the gear indicator worked. Great! I fixed it! Although, I never pulled any fuses, not once did I even open it up while working on the truck.... I was puzzled, but glad at this point. I went for another test drive, expecting great things, to only be let down again... The transmission is slipping BAD, I barely made it up a moderate hill from a stop. Once it got going, it seemed okay, but from a dead stop I could've gotten up to speed faster running.
So if you've read this far, thank you! Is there a "relearn" procedure for the trans TCM and engine ECM?? Is there something I've missed? The transmission has always been strong in this truck. I flushed the entire system and changed the filter earlier this summer before a trip to Florida and back to Kentucky. I don't understand how it could just suddenly, all at once, fail, just after having engine issues. The truck does have 220K miles, but has been very well maintained and serviced. Just wanted to see if I'm missing something, or if anyone has an explanation for missing fuses other than ghosts or gremlins! Thanks in advance!!

 

[Geotrash]

Sounds like a separate issue. The bizarre warning lights and misfire behavior was likely a ground issue. Did you remove any grounds while freeing up your lifter?

On the transmission itself, I think you just experienced a rare double issue at the same time. There are 2 potential issues: check balls in the valve body that shrink over time and get stuck in their ports, causing limited or no forward movement. This is relatively easy to fix with the transmission still in the car. The 2nd is a cracked 1-2-3-4 gear piston.

 

[Doubeleive]

I would double check your work (electrical wise), double check the grounds (all of them) and check the transmission harness if you pulled on it or something there is a tsb for the harness connector having pins come out (https://static.nhtsa.gov/odi/tsbs/2012/SB-10043829-6448.pdf). Also unplug that ecm and check to be sure everything is clean.
it's worth a try... good luck

 

[2011DenaliInKY]

Thanks for the assistance, thus far! I really appreciate you guys taking the time to think my issue over and provide the help you have. I just find it so odd that I would have a failure such as this at the exact same time as the engine problem. The more I think about it, I feel like it has to be something I disturbed, more than likely an issue with a harness or connector. When I get off work I'll check all the wiring over very closely.
The truck does move on its own, not totally inoperable, and reverse seems very strong, no slippage at all that I can tell, but from a dead stop, I'm not going to fare well when pulling out into traffic, it just barely moves the truck and if I stay on it, the RPMs just climb and the truck goes no where.

 

[2011DenaliInKY]

So... the truck doesn't have any more warning lights and no check engine light, the engine is smooth, oil pressure and engine temp are right where I want them. I went for a short test drive yesterday just to see if perhaps something changed. With the fluids cold (ambient) the transmission seemed to do okay if I just eased around, but the warmer it got, and more load (like a hill, or my right foot) it started to slip again. Seems to mostly be in the lower gears, or that's all I can tell anyway, haven't gotten it above 60 mph or so and for no real duration of time.
With all that being said, I believe it's probably not an electrical issue, but a mechanical issue. Just wanted to throw it out there one more time to see if maybe someone may know something I don't. I just find it so hard to believe that I can park a perfectly running transmission, for 2 weeks for some engine repairs, and now the trans is just shot. Seems too weird for me to fully accept... Any advice is appreciated greatly - Thanks!

 

[donjetman]

Drop the pan and change the filter. Maybe the front pump is starving for fluid because the filter is too restrictive/clogged? or maybe the pump isn't putting out enough volume and/or pressure to engage the clutch packs properly(bad pump)?

 

[THarber]

When you change ECM's you have to do a re-learn for the BCM and TCM along with a host of other things.

Start here, it might not be specific to your truck but its a start.

GM Computer Relearn Procedure - LS1TECH - Camaro and Firebird Forum Discussion

PCM Diagnostics & Tuning - GM Computer Relearn Procedure - GM Computer Relearn Procedure (including Crankshaft relearn) Here are the procedures GM uses to do Computer Relearn. This includes CASE (crankshaft variation relearn) GENERAL MOTORS VEHICLE COMPUTER RELEARN PROCEDURES Performing any of...

ls1tech.com

Tim

 

[2011DenaliInKY]

When you change ECM's you have to do a re-learn for the BCM and TCM along with a host of other things.

Start here, it might not be specific to your truck but its a start.

GM Computer Relearn Procedure - LS1TECH - Camaro and Firebird Forum Discussion

PCM Diagnostics & Tuning - GM Computer Relearn Procedure - GM Computer Relearn Procedure (including Crankshaft relearn) Here are the procedures GM uses to do Computer Relearn. This includes CASE (crankshaft variation relearn) GENERAL MOTORS VEHICLE COMPUTER RELEARN PROCEDURES Performing any of...

ls1tech.com

Tim

Thanks Tim, I didn’t have the ECM replaced, I just sent it off and had a guy tune it to turn off the DOD circuit. With this being the case, would you have to do all of the relearn stuff?

 

[2011DenaliInKY]

Sounds like a separate issue. The bizarre warning lights and misfire behavior was likely a ground issue. Did you remove any grounds while freeing up your lifter?

On the transmission itself, I think you just experienced a rare double issue at the same time. There are 2 potential issues: check balls in the valve body that shrink over time and get stuck in their ports, causing limited or no forward movement. This is relatively easy to fix with the transmission still in the car. The 2nd is a cracked 1-2-3-4 gear piston.

Thanks Dave, if a man were to drop the pan and pull the valve body assembly out, is there a kit you’d recommend, or I guess that would depend on what I found. I’m just trying to get my ducks in a row before I pull it apart to take a look. I’ve got limited experience with trans internals, and ive tried to get my interwebs diploma on it, but most of the videos show a unit out of the vehicle all torn apart.

 

[swathdiver]

Howdy Everyone!

This is my first post here, glad to see a group of people sharing knowledge! I've got a 2011 GMC Yukon Denali with the 6.2L and 6L80 transmission. I recently suffered a collapsed intake lifter on the #1 cylinder, but was able to get it freed up using a special tool I learned about from Crazed Performance Repair (check out Charles on YouTube if you've not already) and sent the ECM out to LT1Swap.com to have it tuned to turn the DOD/AFM system off. While waiting for the ECM to return, I changed the plugs and wires and buttoned up the intake and everything else I had apart while freeing up the lifter. So on Monday my ECM arrived back to me, I was tickled to death to get my truck back on the road. I had the battery disconnected the entire time the unit was down, and swapped it out for a new one as well. So I plugged the ECM in, connected my battery, triple-checked all the wiring connections, and fired it up. The engine ran great, smooth idle, no immediate lights on the dash, no lifter ticking or engine misfiring, I'm in business!! So I thought... I pulled out of the driveway and started getting all the typical warnings on the dash "service stabilitrak", "service traction control", "service side blind zone alert system" and a check engine light. When I went to pull out onto the road it just didn't feel right, the engine was smooth, but it was like my transmission was slipping, bad! I noticed that the little indicator on the dash to let you know which gear you're in didn't move with the gear selector. I also noticed the trans temp was not being displayed like it usually did. I made a short trip, maybe half a mile, and came back home, livid! I slept on it Monday night and all day at work on Tuesday I kept thinking what I could've missed. I thought it had to be some communication issue between the TCM and ECM. I emailed the tuner, he claimed it was nothing he could've done. I got home yesterday and looked EVERYthing over again. I pulled open the main fuse panel under the hood and started reading some circuit names and came across a 15 amp fuse for "TCM batt" (I think that was the name, I forgot to snap a pic of it) that was missing a fuse. For the sake of trying it, I put a 15 amp fuse in that spot, then fired it up again. I noticed that I didn't get any of the warnings now, the trans temp was displayed, the gear indicator worked. Great! I fixed it! Although, I never pulled any fuses, not once did I even open it up while working on the truck.... I was puzzled, but glad at this point. I went for another test drive, expecting great things, to only be let down again... The transmission is slipping BAD, I barely made it up a moderate hill from a stop. Once it got going, it seemed okay, but from a dead stop I could've gotten up to speed faster running.
So if you've read this far, thank you! Is there a "relearn" procedure for the trans TCM and engine ECM?? Is there something I've missed? The transmission has always been strong in this truck. I flushed the entire system and changed the filter earlier this summer before a trip to Florida and back to Kentucky. I don't understand how it could just suddenly, all at once, fail, just after having engine issues. The truck does have 220K miles, but has been very well maintained and serviced. Just wanted to see if I'm missing something, or if anyone has an explanation for missing fuses other than ghosts or gremlins! Thanks in advance!!

My first thought is battery. I reckon that the new battery is low on juice or has a bad cell. Charge it up and try again. These trucks go nuts when the voltage is low in any of the modules. Some begin to get squirrely at 11 volts, others go nuts at 9 and so on. This includes the TECHM in the transmission. Check your grounds sure, check the wires and connectors on the battery, making sure they are tight and corrosion free.