1998 GMC Sonoma Owner's Manual - Page 151

Activating theTheft-Deterrent Feature The instructions which follow explainhow to enter your secret code to activate the THEFTLOCK system. It is recommended that you read through all nine steps before starting the procedure. 6. Press MN again to make the last two digits agree with your code. 7. Press HR to make the first one or two digits agree with your code. 8. Press AM-FM after you have confirmed that the code matches the secret code you have written down. The display will show REP to let you know that you need to repeat Steps 5 through 7 to confirm your secret code. 9. Press AM-FM and this time the display will show SEC to let you know that your radio is secure. The indicator by the volume control will begin flashing when the ignition is turned off. NOTE: If you allow more than 15 seconds to elapse between any steps, the radio automatically reverts to time and you must start the procedure over at Step 4, 1. Write down any three or four-digit nomber from 000 to 1999 and keep it in a safe place separate from the vehicle. 2. Turn the ignition to ACCESSORY or RUN. 3. Turn the radio off. 4. Press the 1 and 4 buttons together. Hold them down until --- shows on the display. Next you will use the secret code number which you have written down. 5. Press MN and 000 will appear on the display. 3-21