GMC 2018

Im a service advisor for chevrolet from my experience when you have low voltage you will get a slew of erroneous eng codes b/c of low volts as for the batt going dead that can be a few things bad ground, dead cell open circuit..... personally i think its the way they have the fuel prime pump set-up to start when you open the door. i dont know why they do it like this. i feel like everytime i walk by one you can hear it buzzing lol.

wow I had the same exact thing happen to me yesterday, Traded in my 19 AT4 5.3 for a 2020 AT4 with the 6.2 and with only 2 miles on it i go to start it and it was slow to turn over. when it did the check eng light came on. I looked at vehicle diagnostics and it had a few voltage codes. so i drove around for about 30 min turned it off waited 20 min and restarted started right up and the check eng light was gone. I was a service advisor for 4 years at a chevy store and from my experience anytime you have a dead or dieing battery you will get a slew of erroneous eng codes b/c there are so many computers on these thing and they are very sensative to how much voltage they get and will fault if its not exactly right.... what is the dealer telling you ?