You can't simply change keys. They have to be programmed into the system.
Try the Passlock relearn procedure.
Use your old key
This may work on the first cycle but if it doesn't, complete all 3 cycles.
30-Minute Relearn Procedure
Use this procedure after replacing the following components:
The passkey III (PK3) keys
The theft deterrent control module
The PCM, see important above
IMPORTANT: This procedure is not available on vehicles equipped with option code (Z49 or BAE).
If replacing a theft deterrent control module with an GM SPO Replacement Part, perform the procedure to setup a new theft deterrent control module prior to the 30-minute relearn procedure.
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.
IMPORTANT: 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.
Tuesday, December 1st, 2015 AT 4:18 PM