I have a 2003 Monte Carlo SS 2.8 and I'm a grandma who needs help. One night I came home and the next morning I couldn't start the car. The battery have been disconnected so I know doesn't it have to be reprogrammed to the brain and the security light went on and I can't get past that I tried to subscribe to OnStar but I can't connect so OnStar said to talk to the dealership and get a data update for my OnStar and the dealership says they don't know when I'm talking about and they've never done it before now what ?

 

Found a couple of solutions.

https://montecarloforum.com/forum/mo...-system-18529/

PASSKEY LOCKOUT RESET ALL GM CARS 1999 AND UP
1) Put the key in the ignition and turn to the "ON" position. Leave it that way for 10 minutes. After 10 minutes turn the key and take it out. Repeat this process (2) more times (3 times, 30 minutes total) This should reset the PASSKEY system to recognize your key.