Theory Of Operation - Headlamps

The headlight system includes the BCM, the IPC and the left (lighting) multi-function switch on the steering column. The headlight bulbs have a path to ground at all times through their connection to the headlight and dash wire harness. The headlight and dash wire harness has takeouts with eyelet terminals that are secured by screws to the front end sheet metal within the engine compartment. The BCM monitors hardwired inputs to determine the status of the left multi-function switch and whether the headlight high or low beams are selected. The BCM then controls headlight illumination through relays soldered onto the BCM internal circuit board.

When the BCM detects a change in headlight beam selection, the BCM energizes or de-energizes a high side driver, which controls an output to the solenoid that operates the shutter in each headlight. The BCM also sends the appropriate electronic messages to the IPC to control the illumination of the high beam indicator. The BCM remembers which beams (LOW or HIGH) were selected when the headlights were last turned OFF, and energizes those beams again the next time the headlights are turned ON.