2002 GMC Sonoma Owner's Manual - Page 167

To adjust balance or fade to the middle position, select BAL or FAD. Then press and hold AUDIO for more than two seconds until you hear a beep. L and a zero or F and a zero will appear on the display. To adjust both tone controls and both speaker controls to the middle position, end out of audio mode by pressing the AUDIO button until the display goes blank. Then press and hold AUDIO for more than two seconds until you hear a beep. CEN will appear on the display. Radio Messages CAL (Calibrated): Your audio system has been calibrated for your vehicle from the factory. If CAL appears on the display it means that your radio has not been configured properly for your vehicle and must be returned to the dealership for service. LOC (Locked): This message is displayed when the TheftlockR system has locked up. Your vehicle must be returned to the dealership for service. AM-FM Stereo with Cassette Tape Player (If Equipped) Playing the Radio Power: Turn the VOLUME knob to turn the system on and off. VOLUME: Turn this knob clockwise to increase volume. Turn it counterclockwise to decrease volume. RECALL: Press this knob to display the station being played or to display the clock. Clock display is available with the ignition turned off. 3-13