Exterior Lighting Systems

Exterior Lighting Systems Description and Operation

Exterior Lamps

The exterior lighting system consists of the following components:

* Headlamp switch
* Turn signal/multifunction switch
* Brake pedal position sensor
* Body control module (BCM)
* Ambient light sensor
* DRL relay
* Low beam PCB relay
* High beam PCB relay
* Park lamp relay
* Left cornering lamp PCB relay
* Right cornering lamp PCB relay
* Fog lamp PCB relay
* Low beam headlamps
* High beam headlamps
* Park lamps
* Tail lamps
* License lamps
* Marker lamps
* Turn signal lamps
* Cornering lamps
* Stop lamps
* Center high mounted stop lamp (CHMSL)
* Backup lamps
* Front fog lamps

Low Beam Headlamp Operation

The low beam headlamps may be turned ON in 3 different ways:

* When the headlamp switch in the HEAD position for normal operations
* When the headlamp switch is in the AUTO position, for automatic lamp control (ALC)
* When the headlamp switch is placed in the AUTO position, with the windshield wipers ON in daylight conditions, after a 6 second delay

When the headlamp switch is placed in the HEAD position, ground is applied through headlamps ON switch signal circuit to the body control module (BCM), signaling the headlamps ON request. In response to this signal, the BCM applies ground through the headlamp low beam relay control circuit energizing the LO BEAM PCB Relay. With the relay energized, battery voltage is applied through the switch side of the relay, the left and right low beam fuses, and the low beam supply voltage circuits illuminating the low beam headlamps.

High Beam Headlamp Operation

When the headlamp dimmer switch is placed in the high beam position, the headlamp dimmer switch signal circuit to the BCM is pulled low signaling the headlamp high beam request. In response to this signal, the BCM applies ground through the high beam relay control circuit energizing the HIGH BEAM PCB Relay. With the high beam relay energized, battery voltage is applied through the switch side of the relay, the left and right high beam fuses, and the high beam supply voltage circuits illuminating the high beam headlamps. At the same time the BCM sends a serial data message to the instrument panel cluster (IPC) requesting the IPC to illuminate the high beam indicator.

Flash to Pass (FTP)

When the turn signal/multifunction switch handle is pulled toward the driver, the FTP switch is active and the flash to pass switch signal circuit to the BCM is pulled low signaling the flash to pass request. The BCM then turns ON the high beam headlamps, as described above, until the turn signal/multifunction switch handle is released. If the low beam headlamps were ON during FTP operation, they will remain ON.

Daytime Running Lamps (DRL)

The low beam headlamps are used for DRL operation at a reduced intensity. The DRLs will operate only while the engine is running and the headlamp switch is in the AUTO position. When the DRLs are ON, no other exterior lamps such as the parking lamps, tail lamps, etc. will be on when the DRL are being used. The instrument panel will not be illuminated either.

DRL operation is determined by the ambient light sensor and the controlled by the body control module (BCM). The ambient light sensor is a light-sensitive transistor used to monitor outside lighting conditions. The BCM provides a 5-volt reference signal to the sensor. The sensor will vary this voltage signal between 0.2 and 4.9 volts depending on outside lighting conditions. The BCM monitors the ambient light sensor signal circuit to determine if outside lighting conditions are correct for either DRL or ALC operation. When the BCM determines the conditions are met for DRL operation, it applies ground to the DRL relay control circuit energizing the DRL Relay. With the relay energized, battery voltage is applied through the switch side of the relay, the DRL fuse, and a resistor wire spliced to the low beam supply voltage circuit illuminating the headlamps at a reduced intensity. Any function or condition that turns on the headlamps will cancel DRL operation.

When the BCM detects low light conditions, it will turn OFF the daytime running lamps and turn ON the low beam headlamps as described above in Low Beam Headlamp Operation. The BCM will also turn ON the low beam headlamps in daylight conditions when the windshield wipers are turned ON.

Park, Tail, Marker and License Lamps

The park, tail, license, and marker lamps are turned ON when the headlamp switch is placed in either the HEAD or PARK lamp positions, or anytime the automatic light control (ALC) turns the headlamps ON. When the headlamp switch is placed in the park lamp or headlamp positions, ground is applied through the signal circuit to the BCM indicating the park lamp request. In response to this signal, the BCM applies ground through the park lamp relay control circuit energizing the PARK LP PCB Relay. With the relay energized, battery voltage is applied through the switch side of the relay, both park lamp fuses, and the supply voltage circuits illuminating the park, tail, marker, and license lamps.

Turn Signal Lamps

Battery voltage supplied to the body control module (BCM) from the fuses listed below is used for turn signal and hazard lamp operation.

* LT TRN/SIG fuse for the left turn signals
* CTSY/RF TRN fuse for the right front turn signal
* RR TRN/SIG fuse for the right rear turn signal

When the turn signal switch is place in either the LEFT or RIGHT position, ground is applied through the turn signal switch signal circuit to the BCM indicating the turn signal request. In response to this signal, the BCM applies a pulsating voltage to the front and rear turn signal lamps supply voltage circuits cycling the lamps ON and OFF. At the same time the BCM sends a serial data message to the instrument panel cluster (IPC) to cycle the appropriate turn signal indicator ON and OFF.

Hazard Lamps

The hazard flashers may be activated in any power mode. When the hazard switch is placed in the ON position, ground is applied through the hazard switch signal circuit to the body control module (BCM) indicating the hazard lamps ON request. In response to this signal, the BCM applies a pulsating voltage to all front and rear turn signal lamps supply voltage circuits cycling the lamps ON and OFF. The BCM also sends a serial data message to the instrument panel cluster (IPC) to cycle both turn signal indicators ON and OFF.

Cornering Lamps

Without Vehicle Stability Enhancement System (VSES)

The left and right cornering lamps are located within the headlamp assemblies. The BCM will illuminate the cornering lamp only during turn signal operation. When a left or right turn signal is activated, the BCM applies ground to the appropriate cornering lamp relay control circuit energizing the LF or RF CRN LAMP PCB RELAY. With the relay energized, battery voltage is applied through the switch side of the relay, the CRN LAMP fuse, and the cornering lamp supply voltage circuit illuminating the cornering lamp until the turn signal is turned OFF.

With Vehicle Stability Enhancement System (VSES)

On vehicles equipped with VSES the cornering lamps will illuminate when a turn signal lamp is activated or a change in steering wheel direction. When a left or right turn signal is activated, the BCM applies ground to the appropriate cornering lamp relay control circuit energizing the LF or RF CRN LAMP PCB RELAY. With the relay energized, battery voltage is applied through the switch side of the relay, the CRN LAMP fuse, and the cornering lamp control circuit illuminating the cornering lamp until the turn signal is turned OFF. The cornering lamps will also illuminate when the steering wheel is turned a 1/4 turn to the left or right without a turn signal being activated. The BCM receives a serial data message from the electronic brake control module (EBCM) indicating the steering wheel position. The EBCM receives steering wheel positions via the steering angle sensor. When the BCM receives the serial data message from the EBCM that the steering wheel has changed position a 1/4 turn or greater in either direction and the vehicles speed is greater than 12.8 km/h (8 mph), the BCM will respond by applying ground to the appropriate cornering lamp relay control circuit energizing the LF or RF CRN LAMP PCB RELAY. With the relay energized, battery voltage is applied through the switch side of the relay, the CRN LAMP fuse, and the cornering lamp control circuit illuminating the appropriate cornering lamp until the steering wheel returns to the straight or home position.

Stop Lamps

The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The body control module (BCM) provides a 5-volt reference voltage and low reference to the brake pedal position sensor. The position sensor provides an analog voltage signal back to the BCM that will increase as the brake pedal is applied. When the brake is applied, the BCM will then apply battery voltage to the left and right stop/turn signal lamp supply voltage circuits and the center high mounted stop lamp (CHMSL) supply voltage circuit illuminating the stop lamps. At the same time the BCM applies battery voltage through the signal circuit to the transmission control module (TCM) and the engine control module (ECM) indicating that the brakes are applied.

The stop lamps on this vehicle will not illuminate unless the ignition is in the accessory, run, or crank positions. When the ignition is in the OFF position the stop lamps will not illuminate when the brake pedal is applied.

Battery voltage from the LT TRN/SIG and RT TRN/SIG fuses located in the rear fuse block is also used by the body control module (BCM) for stop lamp operation.

Backup Lamps

Battery voltage from the CHMSL/BCK-UP fuse located in the rear fuse block is supplied to the body control module (BCM) for backup lamp operation. When the gear selector is placed in to the REVERSE position, the powertrain control module (PCM) sends a serial data message to the BCM indicating that the gear selector is in the reverse position. The BCM then applies battery voltage to the backup lamp supply voltage circuit illuminating the left and right backup lamps. The engine may need to be running for the backup lamps to function.

Front Fog Lamps

When the fog lamp switch is turned ON, ground is applied through the fog lamp switch signal circuit to the body control module (BCM) indicating the fog lamp request. In response to this signal, the BCM applies ground to the fog lamp relay control circuit energizing the FOG LAMP PCB Relay. With the relay energized, battery voltage is applied through the switch side of the relay, the FOG fuse, and the fog lamp supply voltage circuits illuminating the fog lamps. At the same time the BCM sends a serial data message to the instrument panel cluster (IPC) requesting that the fog lamp indicator be illuminated.

Battery Rundown Protection/Inadvertent Power

The BCM controls the lighting system through circuits that enable the exterior lamp functions of the park lamps, the head lamps, the fog lamps, and the interior lamps. The BCM opens these enabling circuits 10 minutes after the ignition switch is turned OFF with no lamp switch activity. If the ignition switch is turned to any position other than OFF, or if a lamp switch is activated during this time period, the timer resets for another 10 minutes.