Principles of Operation

PRINCIPLES OF OPERATION

The signal duty cycle is varied in proportion to the demanded instrument panel dimming level detected by the lighting control module (LCM) from the instrument panel dimmer switch.

The following components have fixed level backlighting that is illuminated when the ignition is in the RUN or ACCESSORY position:
- driver and passenger front and rear power window switches
- driver and passenger power door lock switches

The backlighting for the keyless keypad switch is controlled by the driver door module.

If the headlamps are operated during daylight hours the light sensor amplifier will detect high ambient light levels and signal the LCM to keep illumination levels readable and therefore are non-adjustable on the following components:
- audio unit
- EATC unit

Dimmable backlighting is a pulse-width modulation (PWM) power source, provided by the LCM, when the headlamp switch is set to the parking lamps ON or headlamps ON position or the autolamp function is enabled. Light intensity is adjusted by rotating the instrument panel dimmer switch.

When the headlamp switch is in the OFF position, the instrument cluster internally powers the gauge illumination lamps to full brightness. When the headlamp switch is in the ON position, the gauge illumination lamps are powered by the LCM. The message center backlighting intensity is set by the instrument cluster and controlled by the standard corporate protocol (SCP) message from the LCM.

The LCM provides 2 SCP signals to indicate backlighting intensity to the following:
- EATC
- overhead console

These modules use the SCP message to dim their respective displays.

The LCM provides a pulse width modulated (PWM) output to control backlighting intensity to the following:
- cigar lighter
- message center switch
- steering wheel control switches
- window and lock switches
- headlamp switch
- mirror switches
- electric clock