Headlamps

Headlamps

Principles of Operation

Exterior Lighting

The headlamp switch is integrated into the Front Lighting Control Module (FLM). The FLM (Front Lighting Control Module) monitors the headlamp switch position and sends a message over the High Speed Controller Area Network (HS-CAN) to the Body Control Module (BCM) to indicate the headlamp switch status (position or a fault with the headlamp switch).

If the BCM (Body Control Module) detects a fault from the headlamp switch or loses communication with the FLM (Front Lighting Control Module), the BCM (Body Control Module) turns the parking lamps and headlamps on and keeps them on until the battery saver feature times out.

Refer to Exterior Lighting Exterior Lighting in the Description and Operation for information regarding the battery saver feature.

If either situation occurs, the BCM (Body Control Module)cannot be ruled immediately as being at fault. This is normal behavior of the BCM (Body Control Module) design as a fault has been detected with the inputs from the headlamp switch.

When the BCM (Body Control Module) receives input requesting the headlamps on, it supplies voltage to the headlamp bulbs (halogen headlamps) or the ballasts (High Intensity Discharge (HID)) within each headlamp assembly.

High Beam and Flash-to-Pass

The Steering Column Control Module (SCCM) monitors the multifunction switch for a flash-to-pass or high beam request. When the multifunction switch is in the FLASH-TO-PASS or HIGH BEAM position, the SCCM (Steering Column Control Module) sends a message to the BCM (Body Control Module) to indicate the request.

When the low beams are on and the BCM (Body Control Module) receives a request for high beams (or a flash-to-pass request), the headlamps remain powered and a shutter within each headlamp is activated. This changes the headlamp beam pattern to illuminate a greater distance.

When the low beams are off and the flash-to-pass is requested, the headlamps and the shutters are activated for approximately 0.5 second. When the low beams are on and the flash-to-pass is requested, the shutters within the headlamps are activated as long as the multifunction switch is held in the FLASH-TO-PASS position.

Field-Effect Transistor (FET) Protection

The Field-Effect Transistor (FET) protection strategy prevents module damage in the event of excessive current flow. For additional information of the FET (Field-Effect Transistor), refer to Body Control Systems.

The BCM (Body Control Module) FET (Field-Effect Transistor) protected output circuits for the headlamp system are both low and high beam output circuits.