Same thing just happened to my 24, AT4X HD the other day. 20,000kms , I was able to get it in the dealer and they had it for 4 days and could not figure out the issue. Called me this morning and said they noted it in my file in case it happens again. The following items below do not work when the warning lights and check engine lights come on.
-engine break stops working
-traction control
-off road mode
-tow /haul mode
-remote start as stated in previous poster.
truck also down shifts very hard when these lights are on. I’m beyond frustrated with GMC on the new 2024 trucks. My dealer /service department has been amazing to deal with thank goodness. They are trying to figure it all out but so far no luck on diagnosing the problem.
