Headlamps

Headlamps

Overview

The headlamp system consists of:

- Headlamp assemblies

- Ballasts (HID (High Intensity Discharge) only)

- Headlamp switch (integrated into the FLM (Front Lighting Control Module))

- Multifunction switch

- BCM (Body Control Module)

- SCCM (Steering Column Control Module)

The headlamp system is a dual-beam pattern system. It consists of a single replaceable headlamp bulb in each headlamp assembly. The vehicle may come equipped with halogen or HID (High Intensity Discharge) bulbs. The park/turn and side marker lamps are integrated into the headlamp assembly.

System Operation

System Diagram





Network Message Chart

BCM (Body Control Module) Network Input Messages






Battery Saver

NOTE: The battery saver time-out is 1 minute if the vehicle has less than 201 km (125 mi).

NOTE: The battery saver does not control the parking lamps if the headlamp switch is in the PARKING LAMPS ON position.

To save battery voltage, the BCM (Body Control Module) provides automatic shut-off of the interior and exterior lamps after a time-out period when the ignition is off. The BCM (Body Control Module) monitors the ignition state and input from the RKE (Remote Keyless Entry) system to determine when to energize or de-energize the battery saver relay and to shut the power off to the lamps. A timer in the BCM (Body Control Module) starts when:

- the ignition changes to OFF,

- any door or liftgate becomes ajar while the ignition is off,

- an UNLOCK button of the RKE (Remote Keyless Entry) transmitter is pressed while the ignition is off,

- a valid keypad code is entered while the ignition is off,

- or the courtesy lamp switch (integrated into the FLM (Front Lighting Control Module)) is used to turn the courtesy lamps on while the ignition is off.

When 10 minutes have elapsed, the BCM (Body Control Module) automatically shuts off voltage to the lamps. The timer restarts (voltage is restored if the BCM (Body Control Module) is in battery saver mode) if:

- the ignition transitions out of OFF,

- any door or liftgate becomes ajar,

- the UNLOCK button of the RKE (Remote Keyless Entry) transmitter is pressed,

- a valid keypad code is entered,

- the courtesy lamp switch is pressed.

Low Beams

The headlamp switch is integrated into the FLM (Front Lighting Control Module). The FLM (Front Lighting Control Module) monitors the headlamp switch position and sends a headlamp switch status message over the communication network to the BCM (Body Control Module) 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 Battery Saver). 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 ( HID (High Intensity Discharge) headlamps) within each headlamp assembly.

Vehicles with halogen headlamps use single filament bulbs.

Vehicles with HID (High Intensity Discharge) headlamps utilize ballasts to provide the necessary voltage to illuminate the HID (High Intensity Discharge) bulbs.

The BCM (Body Control Module) also provides an overload protection of the low beam output circuits. When an excessive current draw is detected, the BCM (Body Control Module) disables the affected low beam circuit driver. REFER to Field Effect Transistor (FET) Protection Description and Operation.

High Beams

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

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

The BCM (Body Control Module) also provides an overload protection of the high beam output circuits. When an excessive current draw is detected, the BCM (Body Control Module) disables the affected high beam circuit driver. REFER to Field Effect Transistor (FET) Protection Description and Operation.

Flash-To-Pass

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

When the low beams are off and the flash-to-pass is requested, the headlamp bulbs 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.

Component Description

Headlamp Assembly

The headlamp assembly has an integrated solenoid activated shutter which changes the headlamp beam pattern when activated. The solenoid and shutter are not serviceable separately from the headlamp assembly. The headlamp assembly is provided power on independent circuits for the low beams and the high beams.

On vehicles equipped with HID (High Intensity Discharge) headlamps, a ballast is located within each headlamp assembly.

Lamp Assembly Condensation

Exterior lamps are vented to accommodate normal changes in pressure. Condensation can be a natural by-product of this design. When moist air enters the lamp assembly through the vents, there is a possibility that condensation can occur if the temperature is cold. When normal condensation occurs, a thin mist forms on the interior of the lens. The thin mist eventually clears and exits through the vents during normal operation. The amount of time it takes to clear the lens of acceptable mist varies with ambient humidity and lamp types. Normal condensation clears from any lamp in 48 hours under dry conditions.

Do not replace a lamp assembly with acceptable levels of condensation such as:

- presence of thin mist (no streaks, drip marks or droplets are present)

- fine mist covers less than 50% of the lens

Examples of unacceptable moisture (usually caused by a lamp housing leak):

- water puddling inside the lamp

- large water droplets, drip marks or streaks present on the interior of the lens

Ballast

There is a ballast located within each headlamp assembly. They are provided power at all times. The ballasts provide high voltage to the HID (High Intensity Discharge) bulbs when a voltage signal is detected from the BCM (Body Control Module).

Front Lighting Control Module (FLM)

The FLM (Front Lighting Control Module) monitors the headlamp switch (integrated into the FLM (Front Lighting Control Module). When the FLM (Front Lighting Control Module) detects the headlamp switch is in the HEADLAMP ON position (or a fault with the headlamp switch), it sends a message over the communication network to the BCM (Body Control Module), indicating the headlamp switch position or a fault with the headlamp switch input.