2023 Sierra 1500 electrical issues

fortim · September 20, 2023

3.0l Duramax with 1,400 miles on it and during normal driving the transmission shuddered going from 2nd to 3rd and went into limp mode with "Service Transmission" and CEL displayed. I was able to pull away normally (it went out of limp mode) after a stoplight. After 3 power cycles, CEL reset, and all was good.
Two days and 100 miles later, the same thing happened, and now I have these messages...

Messages on the DIC:
"Service Transmission"
"Service Emissions System"
"175 mi Until 65 MPH Max Speed"

The dealer pulled the codes and they were for different systems, Trans., emissions, etc. I've read about the wiring harness issue but the dealer has been unable to find any issue with rubbing on the outside of the harness. They've been working with GM Tech and they want to get into the wiring harness looking for a bad connection/broken wire. The truck was built 12/22 and I purchased 7/23.

Are there any TSB's for the wiring harness issue(s)? Has anybody else gone through this? TIA.

64BAwagon · September 20, 2023

these trucks are very complex electronically. An issue like that will require diagnosis by someone skilled at it. If GM tech is involved they will be able to walk the tech through the diagnostics. All it takes is one connector to be wonky to cause several issues. Its going to be a process. As frustrating as it is your patience and cooperation will go a long way with the tech.

fortim · September 21, 2023

Update looks like the issue is between one of the DPF sensors and the Coolant-Flow control valve sensor wiring. Evidently, the sensors share a common wire in the circuit and GM is "thinking" there's an issue there.

The dealer has completed the diagnostic ladder and is taking direction from GM Tech. Two weeks and counting...

fortim · September 26, 2023

It looks like we have a resolution, The dealer found a DPF pressure sensor wire with the insulation (and harness) chaffed. This was in the back of the engine down low, per the dealer "not in the usual place(s)". Supposedly there's a specific procedure to repair the wire and harness. The dealer will also reposition the main engine harness.

Obviously, I have concerns moving forward as this will be our tow vehicle...

The dealer was great to deal with even giving me a new Sierra Elevation as a loaner for three weeks.

silveradosid · September 27, 2023

thx for the update and resolution

Sqrls · September 29, 2023

I had the same exact transmission issue (same shift but no service trans) until tonight’s update. Update said it failed, gave me service 4wd, but fixed the trans issue. Drives like a dream now.

badluckgmowner · January 6, 2025

I had the same issue with my AT4. It happened to me 5 times, on I4 going 65-70 mph. It was repaired 4 times over the course of a year. It was declared a lemon after the 5th time. GM then turned around and sold the truck with a 1-year warranty. I found out today my OnStar info is still associated with the truck.

I switched to a 2024, 5.3 V8. The truck physically turned off on me three different times when I would pull into my driveway.

Unfortunately, GM has a serious issue with quality right now. I'm posting now to share story.