2005 GMC Yukon Owner's Manual - Page 228

To adjust both tone controls and both speaker controls to the middle position, first end out of audio mode by pressing another button, causing the radio to perform that function or by waiting five seconds for the display to return to time of day. 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 the vehicle is a regular cab model. Radio with CD Radio Messages CAL (Calibrated): The audio system has been calibrated for your vehicle from the factory. If CAL appears on the display it means that the radio has not been configured properly for your vehicle and must be returned to your GM dealer for service. LOC (Locked): This message is displayed when the THEFTLOCK® system has locked up. Take the vehicle to your GM dealer for service. If any error occurs repeatedly or if an error cannot be corrected, contact your GM dealer. Base Radio Shown, Bose® Similar If your vehicle has the Bose® audio system, your vehicle will have six Bose® amplified speakers. 3-78