Scuubz

2021 Sierra 1500 AT4. For what it's worth, for when those of you that become stranded. This also has happened to me on numerous occasions. I have sort of found a " cheat code " during the inconvenient moment so that i am not left stranded during those times. Instead of waiting the 30 minutes to try and reprogram the key, Push and HOLD the start button for 12 seconds, then hit the lock and unlock button on the fob (separately). After this, the truck should no longer be in the relearn mode and should start like normal. (Brake pedal + start button.) This does not solve the root cause. It should get you on your way until you are able to determine the fix. TL;DR If push button does nothing, - Press and Hold start button for 12 seconds, then release. - Press the KEYFOB Lock button one time then the unlock button one time. - Then press brake and push button like normal. I hope this helps others who have been and recently started having this issue and been searching the interwebs. cheers.