Description And Operation: Operation

The headlamp switch uses a single resistor multiplexed output to control the many functions and features it provides. The switch receives a clean ground from the Body Control Module (BCM) on a headlamp switch Multiplex (MUX) return circuit. The BCM then reads the switch outputs using an internal pull up on the headlamp/fog lamp switch signal circuit to control the exterior lighting functions.

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

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 BCM over the headlamp/fog lamp switch signal circuit, and 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 HSDs and by sending an electronic confirmation message to the IC over the CAN data bus, which controls the high beam indicator as appropriate. The BCM also remembers which headlamp beams were last selected with the lamp switch, and energizes those beams by default the next time the headlamps are turned ON. If the vehicle is equipped with optional automatic headlamps and the AUTO (Automatic) position is selected, the BCM monitors an electronic ambient light level message received over the Local Interface Network (LIN) data bus from the Light Rain Sensor Module (LRSM) to turn the exterior lighting ON and OFF automatically while the ignition switch status is ON. If vehicle is not equipped with a RLSM,/LSM/RSM but is equipped with auto head lamps, the BCM also monitors for an electronic ambient light level message received over the CAN data bus from the air conditioner - heater control module based upon a hard wired input from the sun sensor.
• Fog Lamps Control  - For vehicles so equipped, the rotary knob on the headlamp switch is depressed to activate or deactivate the optional fog lamps. If the vehicle is equipped with both front and rear fog lamps, the rotary knob is depressed once to activate only the front fog lamps, a second time to activate the rear fog lamps, a third time to deactivate the rear fog lamps and a fourth time to deactivate the front fog lamps. The rear fog lamps can only be illuminated in combination with the front fog lamps. The headlamp switch provides the appropriate resistor multiplexed output to the BCM over the headlamp/fog lamp switch signal circuit, and the BCM reads and responds to this input by energizing or de-energizing the right and left front and rear fog lamp control circuits through internal HSDs and by sending an electronic confirmation message to the Instrument Cluster (IC) over the Controller Area Network (CAN) data bus, which controls the front and rear fog lamp indicators as appropriate.

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