Headlamp: Description and Operation

The headlamp system includes the EMIC, the FCM, the multi-function switch on the steering column and the headlamp switch on the instrument panel. The headlamp bulbs have a path to ground at all times through their connection to the headlamp and dash wire harness. The headlamp and dash wire harness has takeouts with eyelet terminals that are secured by ground screws to the right (right headlamp bulb) and left (left headlamp bulb) inner fender support within the engine compartment. The EMIC monitors a hard wired multiplex input to determine the status of the headlamp switch, and a hard wired multiplex input from the multi-function switch to determine whether the high or low beams are selected. The EMIC then sends the appropriate electronic headlamp switch and headlamp beam select switch status messages to the FCM over the PCI data bus.

The FCM responds to these messages by providing a pulse width modulated voltage output to the proper headlamp bulb through the right and left low and high beam output circuits to illuminate the selected headlamp filaments. The FCM also remembers which beams (low or high) were selected when the headlamps were last turned Off, and energizes those beams again the next time the headlamps are turned On. The EMIC provides a battery saver (load shedding) feature for the headlamps, which will turn these lamps off if they are left on for more than about five minutes with the ignition switch in the Off position. The EMIC provides a fail-safe feature for the headlamps, which will send an electronic message to the FCM to turn the low beam headlamps On automatically if it detects no input from the headlamp switch. Each headlamp includes an integral reflector adjustment screw to be used for static aiming of the headlamps.