i got this info and would like some to try it to see if it works:

1. Press and hold preset buttons 2 & 3 for 6 seconds or until the the first three digits are displayed

2. Write them down

3. Press the AM/FM button the next three digits of the code are displayed

4. Write them down

-If the display reads "INOP" the radio must be powered up for 1 hour before the backup code can be displayed, this means key on, not the engine.
-If you have a scambled back up code, you must call your local GM dealer to get the unlock code.

-To remove the code:

1. Press the HR (hours) button to display "000"

2. Set the first two digits (0-19) of the code with the HR button

3. Set the next two digits (0-99) with the MIN (minutes) button

4. Press the AM/FM button to enter the code

-If done right and the radio unlocks the clock will be displayed

If this works, please post here so that everyone will know that it works, we don't need to pay the dealerships if we don't have to