1995 GMC Yukon Owner's Manual - Page 178

To Lock The System: 1. Write down any number from 000 to 999 and keep it in a safe place. 2. Turn the ignition to ACC or RUN. 3. Turn the radio off. 4. Press the 1 and 4 buttons together. Hold them down until shows on the display. You are now ready to enter your secret code.Don't wait more than 15 seconds between any of the following steps.If you do, the radio automatically returns to time display and you must start the procedure over atstep 4. 5. Press MIN and "000" will appear on the display. 6. Press the MIN button 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 one you wrote down. rEP appears in the display, indicating that you need to repeat steps5 through 7. 9. Press AM/FM and this time the display will show "SEC". "SEC" means the system is secured. With the ignition off, the THEFTLOCK indicator will flash. To Unlock THEFTLOCK After Power Loss a When battery power is reapplied to a secured radio, the radio won't turn on and "LOC" will appear on the display. Enter your secret code as follows. Pause no more than I5 seconds between steps. 1. Turn the ignition on. 2. Turn the radio off. 3. Press MTN and "000" will appear on the display. 4. Press the MIN button again to make the last two digits agreewith your code. 5. Press HR to make the first one or two digits agree with your code. 6 . Press AM/FM after you have confirmed that the code matches the one you wrote down. SEC appears in the display indicating that the radio is now operable. 3-18