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 return circuit. It then provides outputs to the EMIC on a headlamp 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 return 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 headlamp switch illumination control circuit. The EMIC controls this output based upon the dimmer signal select mux 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 internal 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 an output to the EMIC, and the EMIC responds 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 front fog lamps and by sending an electronic message back to the EMIC to control the front fog lamp indicator.
- 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 an output to the EMIC, and the EMIC responds 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 park lamp and the high or low beam headlamp circuits, and by sending an electronic message back to the EMIC to control the high beam indicator. 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.
- 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 an output to the EMIC, and the EMIC responds by providing the appropriate interior lighting control outputs through its internal courtesy lamp driver circuits, electronic dimming level messages to other modules over the CAN data bus, and the proper PWM outputs to control dimming levels through several panel dimmer illumination control driver circuits.

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.