Exterior Lighting - System Operation and Component Description: Headlamps
System Diagram
Network Message Chart
BCM Network Input Messages
| Broadcast Message | Originating Module | Message Purpose |
|---|---|---|
| Headlamp flash to pass status | GWM | Indicates to the BCM a request for the high beams or flash-to-pass. |
GWM Network Input Messages
| Broadcast Message | Originating Module | Message Purpose |
|---|---|---|
| Headlamp flash to pass status | SCCM | Indicates to the GWM a request for the high beams or flash-to-pass. |
| Auto high beam request | IPMA | Indicates to the GWM a request for the high beams based on the IPMA camera input. |
Low Beams
The BCM monitors the headlamp switch position by sending voltage signals on multiple circuits to the headlamp switch. There is one circuit for each headlamp switch position. At any given time, one of the signal circuits is switched to ground to indicate the headlamp switch position.
The BCM turns the parking lamps and headlamps on when the ignition is in RUN and the BCM detects a fault from the headlamp switch or wiring. This is normal behavior of the BCM when a fault has been detected with the inputs from the headlamp switch.
When the BCM receives a message requesting the headlamps on, it supplies voltage to the headlamp bulbs (halogen headlamps) or the ballasts (LED headlamps) within each headlamp assembly.
Vehicles with LED headlamps utilize a ballast, mounted to each headlamp assembly, that controls the voltage to the high beam, low beam, parking and turn Light Emitting Diodes (LEDs) within the headlamp assembly and the low beam DRL function.
The BCM also provides Field Effect Transistor (FET) protection of the exterior lamps switched voltage and low beam output circuits. When an excessive current draw is detected, the BCM disables the affected circuit driver.
Refer to: Module Controlled Functions - Overview .
High Beams
The SCCM monitors the LH steering column multifunction switch for a high beam request. When the LH steering column multifunction switch is in the HIGH BEAMS position, the SCCM sends a message over the HS-CAN2 to the GWM, then the GWM sends the message to the BCM over the HS-CAN1.
When the low beams are on and the BCM receives a request for high beams, the low beam bulbs (halogen headlamps) or low beam Light Emitting Diodes (LEDs) (LED headlamps) remains powered on and the high beam bulbs (halogen headlamps) or high beam Light Emitting Diodes (LEDs) (LED headlamps) are also illuminated.This changes the headlamp beam pattern to illuminate a greater distance.
The BCM also provides Field Effect Transistor (FET) protection of the exterior lamps switched voltage and high beam output circuits. When an excessive current draw is detected, the BCM disables the affected circuit driver.
Refer to: Module Controlled Functions - Overview .
Automatic High Beams
The automatic high beam system uses an interior rear view mirror mounted camera to monitor surrounding traffic conditions and high beam usage. The camera is hardwired to the IPMA and serviced with the interior rear view mirror assembly. The IPMA communicates light information over the HS-CAN2 to the GWM then the GWM sends the information to the BCM over the HS-CAN1.
The automatic high beam feature is active only when the headlamp switch is in the AUTOLAMPS position.
During nighttime driving, the automatic high beam system automatically turns the high beams on if it is dark enough and no other traffic is present. When the system detects an approaching vehicle's headlamps or a preceding vehicle's rear lamps, the system turns off the high beams. When the approaching vehicle's headlamps or the preceding vehicle's rear lamps are no longer detected, the high beams automatically turn back on.
Flash-To-Pass
The SCCM monitors the LH steering column multifunction switch for a flash-to-pass request. When the LH steering column multifunction switch is in the FLASH-TO-PASS position, the SCCM sends a message over the HS-CAN2 to the GWM then the GWM sends the message to the BCM over the HS-CAN1.
When the ignition is in RUN and the flash-to-pass is requested, the high beams are activated as long as the LH steering column multifunction switch is held in the flash-to-pass position.
Headlamp Exit Delay
When the ignition is OFF and the LH steering column multifunction switch is placed in the FLASH-TO-PASS position and released, the parking lamps and low beams are illuminated. They remain illuminated until:
- 3 minutes have elapsed with a door open.
- 30 seconds have elapsed after all doors are closed.
- the LH steering column multifunction switch is placed in the flash-to-pass position again.
- the ignition switches to RUN.
Within the 30 second delay and all the doors closed, opening any door results in the 3 minute timer restarting.