Radio Head Unit Dimming
WARNING: This page is about a different car, the 2007 Saturn Sky. However, it is still accessible from the selected car via links, so may be relevant.
GMLAN signal data received by the radio determines the radio dimming and backlighting levels. The radio sets the backlight and VF display dimming to the value indicated by the interior dimming level and interior dimming display level signals in the GMLAN dimming information frame. The radio provides faceplate and control/graphics backlighting in the OFF (RAP inactive) when the exterior lighting VN is activated. The radio display is consistent then with the surrounding devices that use analog pulse width modulation (PWM) dimming to backlight their control/graphics when the power mode is OFF and the park lights are ON.