GMC 2005 Safari Owner's Manual page 162

Unlocking the Theft-Deterrent Feature
After a Power Loss
Enter your secret code as follows; pause no more than
15 seconds between steps:
1. Turn the ignition on. LOC will appear on the
display.
2. Press MN and 000 will appear on the display.
3. Press MN again to make the last two digits agree
with your code.
4. Press HR to make the first one or two digits agree
with your code.
5. Press AM FM after you have confirmed that the
code matches the secret code you have written
down. The display will show SEC, indicating
the radio is now operable and secure.
If you enter the wrong code eight times, INOP will
appear on the display. You will have to wait an hour
with the ignition on before you can try again. When you
try again, you will only have three chances, eight
tries per chance, to enter the correct code before INOP
appears.
If you lose or forget your code, contact your GM dealer.
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Disabling the Theft-Deterrent Feature
Enter your secret code as follows; pause no more than
15 seconds between steps:
1. Turn the ignition on.
2. Turn the radio off.
3. Press and hold the 1 and 4 pushbuttons at the
same time until SEC appears on the display.
4. Press MN and 000 will appear on the display.
5. Press MN again to make the last two digits agree
with your code.
6. Press HR to make the first one or two digits agree
with your code.
7. Press AM FM after you have confirmed that the
code matches the secret code you have written
down. --- will appear on the display, indicating that
the radio is no longer secured.
If the code entered is incorrect, SEC will appear on the
display. The radio will remain secured until the correct
code is entered.
When battery power is removed and later applied to a
secured radio, the radio will not turn on and LOC
will appear on the display.
To unlock a secured radio, see Unlocking the
Theft-Deterrent Feature After a Power Loss earlier in
this section.