Circuit Operation
HEADLAMPSVoltage is applied at all times to the Lamp Control Module (LCM) through the HDLP Fuse 40 and CKT 1242 (RED). When the headlamp switch is depressed, the Headlamps input to the LCM is grounded. The LCM then applies voltage through the HDLOBML Fuse and HDLOBMR Fuse, which feed the LH low beam headlamp and RH low beam headlamp, respectively. When the multi-function lever (turn signal) is pulled towards the driver until it clicks, CKT 524 (PPL) is grounded to the LCM. It then removes voltage from the low beam headlamps and applies voltage through the HDHIBML Fuse and HDHIBMR Fuse, which feed the LH high beam headlamp and RH high beam headlamp, respectively.
FLASH-TO-PASS
When the multi-function lever (turn signal) is pulled towards the driver (but does not click), CKT 307 (YEL) is grounded to LCM. It then supplies voltage to the LH and RH high beam headlamps for as long as the lever is held. The flash-to-pass function will override the low beam headlamps or Daytime Running Lamps (DRL) if either is active.
TWILIGHT SENTINEL
Twilight sentinel determines whether the DRL or the exterior lamps and the low beam headlamps at full intensity should be on based on the reading from the ambient light sensor. When the ambient light sensor indicates daytime, the twilight sentinel turns on the DRL. When the ambient light sensor indicates darkness, the twilight sentinels turn on the exterior lamps and the low beam headlamps at full intensity. The twilight sentinel also keeps the lamps on for a delay period (3 to 180 seconds), when the vehicle is in PARK, the ambient light sensor indicates darkness, and the ignition switch is OFF. The twilight sentinel can be manually held in the OFF position. When it is dark and the gear selector in PARK, pushing the twilight sentinel switch to OFF will turn off the headlamps and exterior lamps. Pushing it to OFF again will turn on the headlamps and exterior lamps. When the gear selector is out of PARK, pushing the twilight sentinel switch will have no affect.
AMBIENT LIGHT SENSOR
The LCM monitors ambient light conditions through the ambient light sensor. The ambient light sensor is a variable resistor whose resistance changes as the ambient light level around it changes. As ambient light decreases the resistance of the ambient light sensor increases. The LCM measures the voltage across the ambient light sensor and determines whether it is day or night.
DAYTIME RUNNING LAMPS (DRL)
When the ignition switch is in RUN, the ambient light sensor indicates daylight, and the vehicle is not in PARK, the DRL are activated. When these conditions have been met, the LCM supplies voltage through CKT 593 (DK BLU) to the high beam headlamps in series. Because the high beam headlamps are in series, they split the voltage supplied by the LCM and they at a reduced intensity. The DRL are disabled if the flash-to-pass feature is activated or if the vehicle is placed in PARK. When the ambient light sensor indicates darkness, the low beams are automatically turn on at regular intensity and the high beam turn off.
PERIMETER LIGHTING
Perimeter lighting provides a personal security feature by illuminating exterior lights on the vehicle exterior for 15 seconds when the keyless entry transmitter is used to unlock the doors and it is dark outside. The backup lamps, headlamps, and park lamps will come on.
When the UNLOCK button on the key fob is pressed, the Remote Function Actuator (RFA) Module grounds CKT 624 (BLK/WHT) to the LCM. The LCM then provides battery voltage to the headlamps and park lamps. The RFA provides ground for the Reverse Relay through CKT 1655 (DK ORN). The coil is energized and the switch contacts close providing voltage to the backup lamps.
Also refer to Exterior Lamps, and Backup Lamps, for Perimeter Lighting schematics.
Testing and Inspection
Backup Lamp