GM Service Manual Online
For 1990-2009 cars only

THEFTLOCK® is designed to discourage theft of your vehicle's radio. The feature works automatically by learning a portion of the Vehicle Identification Number (VIN). If the radio is moved to a different vehicle, it does not operate. If the radio is removed from your vehicle, the original VIN in the radio can be used to trace the radio back to your vehicle.

With THEFTLOCK® activated, the radio does not operate if stolen.