Try this procedure if it doesn't work you will need to have the codes read with a GM scan tool .Before you do the procedure remove both battery cables and hold them together for 30 seconds and have a helper hold the brake pedal down while you are doing it.Reconnect the battery cables and perform the procedure.Hooking up a backup battery or another car running to keep your battery charged would be a good idea during the procedure since it will take 30 minutes or more.
With a master passkey III key (Black), turn ON the ignition, with the engine OFF.
Observe the Security telltale, after approximately 10 minutes the telltale will turn off.
Turn OFF the ignition, and wait 5 seconds.
Repeat steps 1-3 two more times for a total of 3 cycles or 30 minutes.
The vehicle learns the key transponder information and/or passwords on the ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
With a master passkey III key, start the vehicle. The vehicle has now learned the key transponder information and the PCM has now learned the fuel continue password.
With a scan tool, clear any DTCs.
Good luck,Mike.Bonuses are appreciated.