Headlamp Switch - Operation

OPERATION

The headlamp switch uses two resistor multiplexed outputs and one conventional output to control the many functions and features it provides. The switch receives a clean ground from the ElectroMechanical Instrument Cluster (EMIC) (also known as the Cab Compartment Node/CCN) on a headlamp switch MUX return circuit. It then provides outputs to the EMIC on a headlamp/fog lamp switch signal circuit to control exterior lighting functions, on a panel lamps dimmer signal circuit to control panel dimmer and interior lighting functions, and on a cargo lamp switch signal circuit to control the cargo lamps.

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 EMIC on a panel lamps driver circuit. The EMIC controls this output based upon the panel lamps dimmer signal circuit input from the headlamp switch.

The headlamp switch operates as follows:

- Cargo Lamps Control - The cargo lamp push button on the headlamp switch is depressed to activate or deactivate the cargo lamps. The headlamp switch provides an output to the EMIC, and the EMIC responds by providing the appropriate cargo lighting control outputs through its cargo lamp driver circuit.
- Front Fog Lamps Control - For vehicles so equipped, the rotary knob on the headlamp switch is depressed to activate or deactivate the optional front fog lamps. The headlamp switch provides the appropriate resistor multiplexed output to the EMIC over the headlamp/fog lamp switch signal circuit, and the EMIC reads and responds to this input by sending electronic fog lamp switch status messages to the Totally Integrated Power Module (TIPM) over the Controller Area Network (CAN) data bus. The TIPM responds by energizing or de-energizing the right and left front fog lamp control circuits through internal High Side Drivers (HSD) and by sending an electronic confirmation message back to the EMIC, which controls the front fog lamp indicator as appropriate.
- 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 EMIC over the headlamp/fog lamp switch signal circuit, and the EMIC reads and responds to this input by sending electronic exterior lighting switch status messages to the TIPM over the CAN data bus. The TIPM 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 back to the EMIC, which controls the high beam indicator as appropriate. The TIPM 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 vehicle is equipped with optional automatic headlamps and the A (Automatic) position is selected, the TIPM also monitors an electronic ambient light level message received over the CAN data bus from the A/C-heater control module based upon a hard wired input from the sun sensor to turn the exterior lighting ON and OFF automatically while the ignition switch is in the ON position.
- 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 EMIC over the panel lamps dimmer signal circuit. The EMIC 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 hard wired inputs and outputs of the switch may be diagnosed using conventional diagnostic tools and procedures. Refer to the appropriate wiring information.