GMC Sierra Classic 2007 Owner's Manual page 290

To adjust both tone controls and both speaker
controls to the middle position, first exit out of audio
mode by pressing another button, causing the radio
to perform that function or wait five seconds for the
display to return to time of day. Then press and hold
AUDIO for more than two seconds until a beep
sounds. CEN (center) displays.
Adjusting the Speakers (Balance/Fade)
AUDIO: To adjust the balance between the
right and the left speakers, press and release
AUDIO until BAL (balance) displays. Then press
and hold the up or the down arrow to move
the sound toward the right or the left speakers.
To adjust the fade between the front and the rear
speakers, press and release AUDIO until FAD
(fade) displays. Then press and hold the up or the
down arrow to move the sound toward the front
or the rear speakers.
To adjust balance or fade to the middle position,
select BAL or FAD. Then press and hold
AUDIO for more than two seconds until a beep
sounds. B (balance) and a zero or F (fade) and a
zero displays.
290
To adjust both tone controls and both speaker
controls to the middle position, first exit out of audio
mode by pressing another button, causing the radio
to perform that function or wait five seconds for the
display to return to time of day. Then press and hold
AUDIO for more than two seconds until a beep
sounds. CEN (center) displays.
Fade might not be available if the vehicle is a
regular cab model.
Radio Messages
CAL (Calibrated): The audio system has been
calibrated for your vehicle from the factory. If CAL
displays it means that the radio has not been
configured properly for your vehicle and must be
returned to your dealer/retailer for service.
LOC (Locked): This message is displayed when
®
the THEFTLOCK system has locked up. Take
the vehicle to your dealer/retailer for service.
If any error occurs repeatedly or if an error cannot
be corrected, contact your dealer/retailer.