GM Service Manual Online
For 1990-2009 cars only
  1. Press the TUNE/SEL knob to enter the main menu.
  2. Turn the TUNE/SEL knob until SET CLOCK is displayed.
  3. Press the TUNE/SEL knob to select SET CLOCK.
  4. Turn the TUNE/SEL knob to adjust the time setting.
  5. Press the TUNE/SEL knob to update the time. VEHICLE TIME UPDATED will appear on the display.

If the CLOCK/RADIO DISP is configured into one of the configurable keys, pressing the key will switch the display between the radio station frequency and the time. See "Configurable Radio Display Keys" under Radio with Cassette and CD for more information on configuring the keys.