2003 GMC Yukon Owner's Manual - Page 229

To adjust both tone controls and both speaker controls to the middle position, end out of audio by waiting for the display to change to the time display. Then press and hold AUDIO for more than two seconds until you hear a beep. CEN will appear on the display. Fade may not be available if you have a regular cab model. Radio with CD 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 Theftlock® system has locked up. Your vehicle must be returned to the dealership for service. Base Radio Shown, Bose® Similar If your vehicle is equipped with the Bose® audio system, your vehicle will have six Bose® amplified speakers. 3-75