Exterior Lighting - System Operation and Component Description: Headlamps
System Diagram
| Item | Description |
|---|---|
| 1 | HS-CAN |
| 2 | (without push button start) |
| 3 | (with push button start) |
| 4 | LH low beam |
| 5 | LH high beam |
| 6 | RH low beam |
| 7 | RH high beam |
| 8 | BCM |
| 9 | LH headlamp |
| 10 | RH headlamp |
| 11 | SASM |
| 12 | Headlamp switch |
| 13 | LH steering column multifunction switch |
| 14 | IPMA |
| 15 | Ignition switch |
| 16 | Start/Stop switch |
| 17 | LIN |
| 18 | RCM |
| 19 | HCM |
| 20 | LIN |
| 21 | LIN |
| 22 | LIN |
| 23 | (with auto high beams) |
| 24 | (with adaptive front lighting) |
| 25 | (with adaptive front lighting) |
HCM Network Input Messages
| Broadcast Message | Originating Module | Message Purpose |
|---|---|---|
| Vehicle yaw rate | RCM | Indicates to the HCM the yaw rate for dynamic headlamp aiming. |
| Steering wheel direction of rotation | SASM | Indicates to the HCM the direction of the steering wheel rotation for dynamic headlamp aiming. |
BCM Network Input Messages
| Broadcast Message | Originating Module | Message Purpose |
|---|---|---|
| Auto high beam request | IPMA | Indicates to the BCM a request for the high beams based on the IPMA camera input. |
Low Beams
The headlamp switch sends a status message over the LIN circuit to the BCM to indicate the headlamp switch status (position or a fault within the headlamp switch).
If the BCM detects a fault from (or loses communication with) the headlamp switch, the BCM turns the parking lamps and headlamps on. This is normal behavior of the BCM design as 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 (High Intensity Discharge (HID)) within each headlamp assembly.
Vehicles with High Intensity Discharge (HID) headlamps utilize a ballast, mounted to each headlamp assembly, to provide the necessary voltage to illuminate the High Intensity Discharge (HID) bulbs.
The BCM also provides Field Effect Transistor (FET) protection of the low beam output circuits. When an excessive current draw is detected, the BCM disables the affected circuit driver.
Refer to: Module Controlled Functions - System Operation and Component Description .
High Beams
The SASM monitors the multifunction switch for a high beam request. When the multifunction switch is in the high beam position, the SASM sends a message to the BCM over the LIN circuit indicating the request.
For vehicles with halogen headlamps, when the low beams are on and the BCM receives a request for high beams, the low beams remain powered and the high beams are activated. This adds light and changes the headlamp beam pattern to illuminate a greater distance.
For vehicles with High Intensity Discharge (HID) headlamps, when the low beams are on and the BCM receives a request for high beams, the High Intensity Discharge (HID) bulbs remains powered on and the high beam bulbs and the shutter within each headlamp are activated. This changes the headlamp beam pattern to illuminate a greater distance.
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-CAN to the BCM.
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 SASM monitors the multifunction switch for a flash-to-pass request. When the multifunction switch is in the flash-to-pass position, the SASM sends a message to the BCM over the LIN circuit indicating the request.
When the ignition is in RUN and the flash-to-pass is requested, the high beams are activated as long as the multifunction switch is held in the flash-to-pass position.
Adaptive Front Lighting
Adaptive front lighting uses a HCM to command the left/right aiming of the headlamps through the LIN to the headlamp assemblies. The headlamp assemblies contain a module that receives the messages through the LIN from the HCM.
Depending on the inputs received (steering wheel angle and vehicle speed for example), the HCM can command the angle at which the headlamps are aimed (left or right) to improve nighttime visibility around curves. Adaptive front lighting is only activated when the headlamp switch is in the AUTOLAMPS position.
Headlamp Exit Delay
When the ignition is OFF and the 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 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.