Radio Head Dimming
WARNING: This page is about a different car, the 2011 GMC Sierra, 2011 GMC Cab & Chassis Sierra, 2011 Chevrolet Silverado, and 2011 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
Dimming and backlighting levels are determined by the serial data messages the radio receives.