Chevy and GMC Duramax Diesel Forum banner
  • Hey Everyone! Enter your ride HERE to be a part of this months Ride of the Month Challenge!
1 - 3 of 3 Posts

·
Registered
Joined
·
7 Posts
Discussion Starter · #1 ·
A few months ago I posted on here about intermittent shifting issues I was having with my 2011 GMC LML. Someone said to try changing the brake switch and that solved my problems for the time being, but after a few weeks they started coming back again. I was pretty convinced that the problems are electrical, so I wrapped a bare copper wire through the frame of my truck and made it long enough that it would drag on the pavement. As long as I had my truck grounded that way, the transmission would work perfectly! Slowly over time, the issues have been getting worse and are particularly bad when I am towing a trailer. The Dash information centre often flashes the message "check trailer wiring." It got so bad this evening that I could hardly get the truck to go in gear and when it would go in gear, it was usually stuck in either 1st or 3rd, which is not easy towing a trailer around town. So I ditched the trailer and after driving some 30 miles and stopping at least half a dozen times to clear DTC's, the transmission is back to shifting normally. I have several trailers and it doesn't seem to make a difference which trailer I am towing, so I don't think it's in the trailer wiring itself. Is it possible that there is a shortage or bare wire in the trailer wiring harness under the pickup? Or do I have something more major going on, like the TCM going out? Most of the time I have no codes at all. Occasionally i get the P0700, generic shift code, but nothing else to give me a clue where to start. Any input greatly appreciated!
2011 GMC Sierra 3500. Stock except DPF delete, using H&S miniMaxx tuner. Have changed power levels and gone back to stock tuning with no change in tranny issues.
 

·
Premium Member
Joined
·
3,573 Posts
I would want to know what a complete vehicle wide dtc check shows first. If it’s just a P0700 in the TCM, and there isn’t any power/ground/connection issues to/at the TCM, then I would put a TCM in it.
 
1 - 3 of 3 Posts
Top