Dimmer Switch: Description and Operation

I/P Lamp Dimmer
The body control module (BCM) regulates the illumination level of the instrument dial faces and the backlighting of the multifunction display (MFD) and LCDs. The illumination level is transmitted from the BCM via the secondary data bus and the receiving assemblies read the signal and adjust the illumination level accordingly. The BCM illumination drive controls the dash and center console illumination, the display window of the trip computer and the radio illumination. Two momentary contact switches in the headlamp switch ramp the illumination intensity up and down to adjust the level of brightness. The dimmer drives to 100 percent when the ignition is ON and the park lamps are OFF. This enables maximum brightness for the trip computer, HVAC and radio illumination. When the park lamps are switched ON, the dimmer operates according to the previously set percentage value. This intensity value is based on the priority key used. The dimmer control inputs are resistor encoded onto one input line. A 'bright' input occurs when DIM+ is activated and there is a 0 ohm reference to the park lamp control output.

A 'dull' output occurs when DIM- is activated and there is a 2,700 ohm reference to the park lamp control output. The resting point of this line is 5,400 ohms. The system default is 100 percent when the circuit for this line is open. The default dimmer is 100 percent, which occurs if the battery or BCM is disconnected.