Switch, Headlamp: Operation

The headlamp switch uses two resistor multiplexed outputs to control the many functions and features it provides. The switch receives a clean ground from the Instrument Cluster (IC) on a headlamp switch MUX return circuit. It then provides outputs to the IC on a headlamp/fog lamp switch signal circuit to control exterior lighting functions and on a panel lamps dimmer signal circuit to control panel dimmer and interior lighting functions.

The switch illumination circuit receives a path to ground at all times through the left instrument panel ground circuit. The illumination level is controlled by a Pulse-Width Modulated (PWM) output received from the IC on a panel lamps driver circuit. The IC controls this output based upon the panel lamps dimmer signal circuit input from the headlamp switch.

The headlamp switch operates as follows:

• Exterior Lighting Control  - The rotary knob on the headlamp switch is rotated to a detent position to activate or deactivate the exterior lighting. The headlamp switch provides the appropriate resistor multiplexed output to the IC over the headlamp/fog lamp switch signal circuit, and the IC reads and responds to this input by sending electronic exterior lighting switch status  messages to the Body Control Module (BCM) over the CAN data bus. The BCM responds by energizing or de-energizing the right and left park lamp feed circuits and the right and left high or low beam driver circuits through internal High Side Drivers (HSD) and by sending an electronic confirmation message back to the IC, which controls the high beam indicator as appropriate. The BCM also remembers which headlamp beams were last selected with the multi-function switch, and energizes those beams by default the next time the headlamps are turned ON. If the automatic headlamps A  (Automatic) position is selected, the BCM also monitors an electronic ambient light level  message received over the CAN data bus from the A/C-heater control module based upon a hardwired input from the sun sensor to turn the exterior lighting ON and OFF automatically while the ignition switch is in the ON position.
• Fog Lamps Control  - The rotary knob on the headlamp switch is depressed to activate or deactivate the front and rear fog lamps. The headlamp switch provides the appropriate resistor multiplexed output to the IC over the headlamp/fog lamp switch signal circuit, and the IC reads and responds to this input by sending electronic fog lamp switch status  messages to the BCM over the Controller Area Network (CAN) data bus. The BCM responds by energizing or de-energizing the right and left front fog lamp control circuits through internal HSDs and by sending an electronic confirmation message back to the IC, which controls the fog lamp indicators as appropriate.
• Interior Lighting Control  - The thumbwheel on the headlamp switch is rotated to the dome DEFEAT, dome ON, PARADE mode, or one of the six panel dimmer detent positions to control the interior courtesy/dome and panel lamps. The headlamp switch provides the appropriate resistor multiplexed output to the IC over the panel lamps dimmer signal circuit. The IC reads and responds to this input by providing the appropriate control outputs through internal HSDs over the courtesy lamps, panel lamps and reading lamps driver circuits, and by sending appropriate electronic dimming level  messages to other electronic modules over the CAN data bus.

The headlamp switch as well as the hardwired inputs and outputs of the switch may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information.