GM vehicles have a useful anti-theft device called “Theftlock” on their in-built stereos. This renders the stereo useless if someone tries to steal it. Unfortunately, should your battery die or if it's disconnected for too long, this system will engage.
Follow these steps should this happen to you so you can retrieve your code and have a working stereo.
Forewarning: You will only have 15 seconds to complete each of these steps. This is another feature of the “Theftlock” system. Also, make sure you have a pen and paper on hand to write down the code from the system.
1. Put the key in the ignition and turn it to the setting ACC. This will power up the electronic systems in the vehicle. The screen on the stereo should now be reading “LOC”; this shows that the “Theftlock” system has been activated.
2. Depending on the number of preset buttons that are on your radio, press and hold the 1 and 4 preset buttons together for 10 seconds. If you don’t have 4 presets buttons, then press and hold 2 and 3 for 10 seconds.
3. The screen will now read “LOC-XXX”. The XXX will be three numbers. Write these down as they are the first 3 digits of the unlock code.
4. Press the AM/FM button on the radio. If the vehicle doesn’t have one of these, press the BAND button.
5. The screen will now read “LOC-XXX”. The XXX again will be three digits. These are the final three in the six digit code. Write these down.
6. Remove the key from the ignition. You now have the six digit code. You will need to contact your GM dealer with this code. They will issue you with a four digit radio code used to unlock the system. Many may do this for free or will only charge you a small amount. This code will not change, so keep this safe should you need to use it again.
7. Once you have this four digit code, start your vehicle and turn on the radio. Press the HOUR key on the radio and you will notice numbers appearing on the screen. Keep pressing this button until you have the first two numbers in your four digit code on the screen. When you have these two numbers, press the MINUTE button. As with the HOUR button, press this until it shows the last two numbers you have in the unlock code.
8. When you have all four digits correct, press the AM/FM button to unlock the stereo. If your vehicle doesn’t have this, use the BAND button. If this has been done correctly, the screen will now read SEC. This indicates that the stereo is now unlocked.
9. If your screen reads INOP, this means that you have incorrectly input the code too many times. To remove this message, you will need to leave your key in the ON position for one hour. Once the INOP message has gone, you can input the code again.