Radio Theft-Deterrent, Factory Backup Code
WARNING: This page is about a different car, the 2003 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
If the security is activated and the radio is disconnected from battery power, the radio will display LOC. The radio will not turn on until the correct unlocking code is entered. If the customer code is lost or unavailable, refer to the Dealer Communications System bulletin about the unlock procedure.