GM STEREO UNLOCK
Ok, the antitheft system that locks the radio is based upon the VIN code for car it is going into being inputted via a GM factory scanner. That is the ONLY way you will get this radio operational. You will pay about 1/2hr labor for a dealer to do this for you. Again, this is the ONLY way. there are no work arounds, no programming yourself or anything else that will work. This is why the method of holding the 2/3 preset doesnt work
FROM GM SERVICE MANUAL:
RADIO UNLOCK PROCEDURE
The "Theftlock" theft deterrent system is a feature on all base and uplevel radios. There is no need to program a security code into the radio as in past model years. The theft deterrent system now utilizes class 2 serial data to determine if the radio is in the appropriate vehicle. Each time the radio receives the "run" power mode message, it compares the VIN information it has stored to the VIN information received from the dash integration module (DIM) on the class 2 serial data circuit. If a mis-match occurs, the radio display will indicate to the user the radio is locked. Once this takes place, a DTC will set, the radio will not respond to any button presses and become inoperative. The two scenarios able to cause this condition are:
A radio is installed from another vehicle or a new GM audio unit
The DIM is replaced and not properly setup with the correct VIN information for that vehicle
The only way to unlock the radio is by using a scan tool. Always refer to the table in this section to diagnose the "Theftlock" DTC for further information.