Part 3
Exterior Lighting Systems Description and Operation
Rear Fog Lamps
The rear fog lamp relay coil and switch terminals are supplied with battery voltage at all times. Ground is applied at all times to the rear fog lamp switch inside of the turn signal/multifunction switch. When the rear fog lamp switch is placed in the ON position, ground is applied through the rear fog lamp switch signal circuit to the body control module (BCM). Battery voltage is applied at all times from the REAR FOG LAMP fuse to the REAR FOG LAMP relay. The BCM applies ground through the rear fog lamp relay control circuit to the coil side of the REAR FOG LAMP relay causing the relay coil to energize. When the relay is energized, the switch contacts close and battery voltage is applied from the REAR FOG LAMP fuse through the relay, to the rear fog lamps.
The BCM will send a serial data message to the instrument panel cluster (IPC) to enable the rear fog lamp indicator.
Park, Tail, License and Marker Lamps
North America
The rear tail, stop, and turn signal functions are performed by light emitting diodes (LED) in the tail lamp assemblies. The tail lamp assemblies wrap around the corner of the vehicle and serve as the rear side marker. The lower portion of each lamp contains reflectors to alert approaching vehicles for nighttime driving safety. Battery positive voltage is applied at all times to both the coil and switch sides of the LT/POS/LP relay located in the rear fuse block. The turn signal/multifunction switch is suppled with ground at all times. When the headlamp switch is placed in either the HEAD or PARK position, ground is applied to the park lamp signal circuit to the body control module (BCM). The BCM responds by applying ground to the park lamp relay control circuit. This energizes the park lamp relay coil causing the relay switch contacts to close allowing battery voltage to flow through the LT/POS/LP and RT/POS/LP fuses to all of the park, tail, license, and marker lamps.
European
The rear tail, stop, and turn signal functions are performed by light emitting diodes (LED) in the tail lamp assemblies. The tail lamp assemblies wrap around the corner of the vehicle and serve as the rear side marker. The lower portion of each lamp contains reflectors to alert approaching vehicles for nighttime driving safety. Battery positive voltage is applied at all times to both the coil and switch sides of the LT/POS/LP and RT/POS/LP relays located in the rear fuse block. The turn signal/multifunction switch is suppled with ground at all times. When the headlamp switch is placed in either the HEAD or PARK position, ground is applied to the park lamp signal circuit to the body control module (BCM). The BCM responds by applying ground to the left and right park lamp relay control circuits. This energizes the left and right park lamp relay coils causing the relay switch contacts to close allowing battery voltage to flow through the LT/POS/LP and RT/POS/LP fuses to all of the park, tail, license, and marker lamps.
Turn Signal Lamps
Ground is applied at all times to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position, ground is applied to the body control module (BCM) through either the right turn or left turn signal switch circuit. Battery voltage is applied at all times to the BCM. The BCM then applies a pulsating voltage to the front and rear turn signal lamps.
Repeater Lamps
The repeater lamps are on export vehicles only. Each lamp is located in the front fender. The repeater lamps are used as additional turn signal lamps, and operate as described in the Turn Signal/Hazard Flasher Lamps description.
Hazard Flasher Lamps
The hazard flashers may be activated in any power mode. The hazard switch is located on the radio/HVAC control panel. The hazard switch signal circuit is momentarily grounded when the hazard switch is pressed. The BCM supplies battery voltage to all four turn signal lamps in an ON and OFF duty cycle. When the hazard switch is activated, the BCM sends a serial data message to the instrument panel cluster (IPC) requesting both turn signal indicators to be cycled ON and OFF.
Stop Lamps
North America
The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the right and left stop lamp control circuits, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL) control circuit. 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.
European
The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to stop lamp relay coil side control circuit, transmission control module (TCM), engine control module (ECM), and center high mounted stop lamp (CHMSL). When the stop lamp relay receives battery voltage from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage from the STOP LAMPS fuse to illuminate the left and right stop lamps and trailer stop lamps. 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.
Backup Lamps
When the transmission is placed in the REVERSE position, the transmission control module (TCM) sends a serial data message to the body control module (BCM). The message indicates that the gear selector is in the REVERSE position. The BCM applies battery voltage to the backup lamps and inside rearview mirror. The backup lamps are permanently grounded. Once the driver moves the gear selector out of the REVERSE position, a message is sent by the TCM via serial data requesting the BCM to remove battery voltage from the backup lamp control circuit. The engine may need to be running for the backup lamps to function.
Battery Run Down Protection/Inadvertent Power
To provide battery run down protection, the exterior lamps will be deactivated automatically under certain conditions. The body control module (BCM) monitors the state of the headlamp switch. If the park or headlamp switch is ON when the ignition switch is placed in either the CRANK or RUN position and then placed in the OFF position, the BCM initiates a 10 minute timer. At the end of the 10 minutes, the BCM will turn off the control power output to the park and headlamp relay coils, deactivating the exterior lamps. This feature will be cancelled if any power mode other than OFF becomes active. The BCM will disable battery run down protection if any of the following conditions exist. The park or headlamp switch is placed in the ON to OFF position, and back to the ON position during battery run down protection. The BCM determined that the park or headlamp switch was not active when the ignition was turned OFF.