Lamps/Lighting - Exterior (Service Information): Operation: Headlamps

The headlamp system includes the Instrument Panel Cluster (IPC), the Steering Column Control Module (SCCM), the Body Control Module (BCM), the headlamp switch and the multi-function switch on the steering column. The headlamp bulbs have a path to ground at all times through their connection to the FEM wire harness. 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 to the body sheet metal. The BCM will store a Diagnostic Trouble Code (DTC) for any shorts or opens in the headlamp circuits.

The BCM monitors a hard wired multiplex input to determine the status of the headlamp switch. The BCM also monitors electronic headlamp beam select switch status messages received from the SCCM over the CAN data bus. The BCM responds to these inputs by providing a pulse width modulated voltage output to the headlamp through high side drivers on the right and left headlamp feed circuits to illuminate the headlamps, and controls the high and low beam shutter operation through high side drivers on the right and left high beam feed circuits. The BCM also sends the appropriate electronic headlamp beam status messages to the IPC to control the illumination of the high beam indicator.

When the optical horn feature is selected, the low beams will shut OFF about 200 milliseconds after the high beams are activated. The BCM 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 BCM 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 eight minutes with the ignition switch in the LOCK position.

The BCM provides a fail-safe feature for the headlamps, which will cause the BCM to turn the low beam headlamps ON automatically if there is no input available from the multi-function switch. The BCM provides a fail-safe feature for the headlamps, which will turn the low beam headlamps ON automatically if there is no input available from the headlamp switch. The BCM also provides a fail-safe feature for the headlamps that will turn the headlamps ON automatically whenever a loss of CAN bus communication is detected with the ignition switch in the ON position.

Each headlamp includes integral reflector adjustment screws to be used for static aiming of the headlamps.