I'm working on a 6L80 that's in a 2018 Silverado 4.3L with 125k miles, mostly highway. Friends vehicle. The trans has a rough shift after it warms up. It's also got a shudder. Code is P0777. Looking online suggests replacing the solenoid pressure switch films so I dropped the pan and removed the valve body to access the TEHCM. There is no metal in the pan so I'm thinking the torque converter is ok. Removal of the TEHCM showed the orange switch diaphrams are ok after I removed them. The solenoids all have consistent measurements of .8 ohms closed and 12k ohms open. At this point I'm scratching my head on what else to look at?
Just replaced the torque converter. Mine had a little shudder and I drove it for a long time. It progressively got worse. I paid a shop to drop the trans and just replace the tq. Then I dropped the pan to clean it and put in a new filter. Pan had a lot of debris. New fluid. Drives just fine. I tow a boat 3,500lbs and toy hauler 6,900 lbs dry.
The 6L80 has had a variety of issues. The major one was the weak torque converter. The fix was installing a 6L90 converter, but even that wasn’t foolproof. Also, there is a spring in the valve body that breaks and causes the shuddering issues. Lots of info out there on those transmissions and their problems. And btw, there is a 26 state lawsuit against GM on the 6L90s from 2015-19. My 16 Sierra has one of those.
On my 2000 that code also says it can be fluid. At 125K that could be an issue though on mine it occasionally slam shift rather than shudders. Another thing to try is run tow/haul mode and see if it changes things.
Thanks, I did watch those, that guy really knows his stuff Given the discoloration of the fluid in this unit and AndyR1's reply I'm changing my tune on it not being the converter to it being the issue since it wasn't the pressure films being broken. Seems like these transmissions have alot of weaknesses
