Need Unlock Code
The radio has the THEFTLOCK feature if the display reads THEFTLOCK.
This feature is designed to discourage theft of the radio. It operates by
using a secret code in order to disable all the radio functions whenever the
battery power is removed.

This features use is optional. If not used, the system plays normally and
the radio is not protected by the feature. If the security feature is activated,
the radio will not operate if stolen.

When activated, the radio will display LOC in order to indicate a locked
condition anytime the battery power is removed. If the battery loses power
for any reason the radio must be unlocked with the secret code before it
will operate.
Radio Display Says LOC or INOP
Most GM cars and trucks used a theft system to lock the radio when power is
lost, as with a battery replacement.
This system was used from the early 1990's to the early 2000's.
If your radio displays the word LOC or INOP * you can retrieve a set of factory
numbers in the radio that enable us to give you an unlock code.
*  If the radio says INOP, you will have to leave the key in the "ON" position, or let the car run for at least 1 hour before you
attempt any unlock procedure. INOP means a secondary theft lock due to too many false attempts to unlock the radio.