GM Service Manual Online
For 1990-2009 cars only
  1. Determine the correct zone location. Refer to Compass Variance Setup Description .
  2. Use the following procedure in order to display the current compass zone setting:
  3. 2.1. Insert the end of a paper clip into the hole on the bottom of the mirror.
    2.2. Press the calibration switch.
  4. Press and hold the switch for 5 seconds or until a zone number appears in the display.
  5. In order to change the current zone setting, press and hold the calibration switch until the correct zone appears.
  6. Release the switch. The compass direction appears within a few seconds.

The zone settings are not lost when the mirror or ignition switch is turned to the OFF position. The zone requires resetting only when the vehicle is outside of the zone's setting.