Add me to the list of stranded drivers! 2020 GMC Sierra AT4, manufactured 09/20 in Fort Wayne, purchased on October 6th, less than 650-miles. The list price on this vehicle was $62K. Drove the truck to pick up lunch, when I came out, the truck would start, then immediately shut off. After a couple of tries, the starter began cycling continuously with or without my finger on the start button. I had to reengage the start button to get the starter to stop the cycling. Just after the second or third failed start, I got a text from GM that stated the following.
"Diagnostic Alert: Service the engine and transmission system in your 2020 Sierra within 1 day."
So the truck was communicating with the mother ship in Detroit. The check engine light also illuminated on the dash. Full battery power and almost a full tank of gas.
I tried to do an external start with the key fob, but it would not start. Waited about a half an hour and was able to coax it to start by playing with the gas pedal. Drove it straight to the dealership and did not turn it off so that they could run their diagnostics. I was also afraid that if I did turn it off it would not restart.
After running their diagnostics, they stated that it needed a new ECM and they had just received a tech bulletin for this issue two-days prior. I also asked them to do a check of the Under Dash Fuse Box bolts and provided them the number of that tech bulletin. They were a bit confused by this request, so I suspect they did not do all of the diagnostics.
So here I sit with a very expensive truck that is nothing more than a paper weight with no confidence in its dependability or reliability.
Oh by the way, I had already taken the truck in on a warranty issue for bed liner material sprayed all over the right taillight.