GM Service Manual Online
For 1990-2009 cars only

Theftlock mode will activate if a valid VIN is stored in the radio and it does not match the last reported VIN via Class 2 communication. DTC B1780 will set and the DTC will store to radio memory.

If a valid VIN is stored in the radio memory, and a VIN is not reported since battery power for the radio was received, theftlocked mode will activate. As in the previous event, DTC B1780 will set and store to radio memory.

When theftlock is active, and the radio is installed in a different vehicle with the same power mode, the radio will display: Locked - THEFTLOCK Active. If a radio, with theftlock active, is installed in a different vehicle with a different power mode, the radio display will be blank.

DTC B1780 will automatically clear when the radio receives the correct VIN or it may be cleared with the scan tool.

Use the scan tool to clear a previous VIN from radio memory. Once the memory is clear, and the radio is powered up, the radio will automatically capture the vehicle's VIN via the Class 2 communication loop and store it to memory.