GM vehicles have three types of Vehicle Thief Deterrent (VTD) systems, each requiring their own set of relearn procedures. Unless these procedures are correctly performed the vehicle will not start after the PCM has been replaced. The three systems are:
Vehicle Anti-Theft System (VATS), Passkey, & Passkey II – resistive chip ignition key
Passlock – coded lock cylinder
Passkey III – transponder ignition key
How do you know what system your vehicle has?
First, compare your key with the picture below and then download the pdf file at this link to follow the instructions.