Headlamp: Description and Operation
HEADLAMP SWITCHWhen the headlamp switch is placed in the ON position the dash integration module (DIM) headlamp switch input is grounded.
TWILIGHT SENTINEL
The twilight delay switch in the fog lamp switch assembly is supplied a reference voltage and ground reference from the instrument panel module (IPM). The switch is a potentiometer that resistance varies as the switch is moved. The IPM receives an input voltage proportional to the resistance of the potentiometer. The IPM sends a class 2 message to the dash integration module (DIM) indicating the on/off status and delay length for the twilight sentinel. With the twilight sentinel in the ON position the DIM will automatically control the headlamps on/off status depending on the night time/daytime status of the ambient light sensor. The DIM will use the twilight sentinel delay length to know how long to keep the headlamps and park lamps on after the ignition switch transitions from ON to OFF during night time conditions.
LOW BEAM HEADLAMPS
The DIM supplies battery positive voltage to the HDLP LO BM relay coil when the headlamps or park lamps need to be on or when the ignition switch is in the ON position. Battery positive voltage (B+) is always supplied to the HDLP LO BM relay switch through the underhood fuse block. When the headlamps are to be active the DIM supplies a ground to the HDLP LO BM relay control circuit and to the low/high beam switch in the headlamp switch. The coil is energized closing the switch contacts. This supplies battery positive voltage (B+) to the HDLOBML Fuse and HDLOBMR Fuse. HDLOBML Fuse supplies battery positive voltage (B+) to the LH low beam headlamp. HDLOBMR Fuse supplies battery positive voltage to the RH low beam headlamp. The LH and RH low beam headlamp is permanently grounded so both the low beam headlamps have power and ground and then light.
HIGH BEAM HEADLAMPS
The DIM supplies battery positive voltage to the HDLP Hi BM relay coil when the headlamps or park lamps need to be on or when the ignition switch is in ON position. Battery positive voltage (B+) is always supplied to the HDLP HI BM relay switch through the underhood fuse block. When the low beam headlamps are on as described above and then the headlamp dimmer switch is placed in the high beam position, the HDLP HI BM relay coil is grounded. The coil is energized closing the switch contacts. This supplies battery positive voltage (B+) to the HDHIBML Fuse and HDHIBMR Fuse. HDHIBML Fuse supplies battery positive voltage (B+) to the LH high beam headlamp. HDHIBMR Fuse supplies battery positive voltage (B+) to the RH high beam headlamp. The RH high beam headlamp is permanently grounded. The LH high beam headlamp is grounded through the DRL Relay when not energized. Both high beam headlamps have power and ground, and then light.
FLASH-TO-PASS
The flash-to-pass switch is permanently grounded. When the headlamp dimmer switch is pulled toward driver, the flash-to-pass switch in the headlamp dimmer switch closes. The DIM Flash-To-Pass input is grounded. In response to this input the DIM supplies ground to the HDLP HI BM relay coil. The HDLP HI BM relay has battery positive voltage (B+) as described above. The relay is energized closing the switch contacts. The high beam headlamps are supplied battery positive voltage (B+) as described above. If the low beam headlamps are already on they will remain on during flash-to-pass. The high beam headlamps will only remain on as long as the switch is held.
AMBIENT LIGHT SENSOR
The ambient light sensor is supplied a reference ground from the IPM. The sensor is a light sensitive photo transistor that varies in voltage as the outside ambient light level changes. The IPM receives the input voltage and sends a Class 2 message to the DIM and the RIM indicating the daytime/night time status. The DIM uses the daytime/night time status of the ambient light sensor to automatically turn on and off the headlamps with the twilight sentinel on. The RIM uses the daytime/night time status of the ambient light sensor to automatically turn on and off the interior courtesy lamps with the interior lamp switch in the AUTO position.
DAYTIME RUNNING LAMPS
With the daytime running lamps (DRL) programmed to be on the DRL will operate when the ignition switch is in the ON position, the gear selector lever is out of the PARK position, the headlamp switch is in the OFF position and the ambient light sensor indicates daytime conditions. Battery positive voltage (B+) is supplied to the DRL relay coil through the underhood fuse block. Battery positive voltage is supplied through the underhood fuse block FOG/DRL Fuse to the DRL relay normally open switch.
The DRL relay normally closed switch is grounded for normal high beam headlamp operation. When the DIM determines that conditions are right for the DRL, the DIM grounds the DRL relay coil. This energizes the DRL relay coil and closes the switch to the normally open contact. Battery positive voltage (B+) is supplied to the LH and RH high beam headlamps in series. The high beam headlamps split the voltage and each lights at half intensity. Current will follow the path from the DRL relay the LH high beam headlamp, HDHIBML Fuse, HDHIBMR Fuse, the RH high beam headlamp and to ground
KEYLESS ENTRY EXTERIOR ILLUMINATION
When the remote function actuator (RFA) module receives a door unlock command from the remote function actuator transmitter the RFA will send a class 2 message to the dash integration module DIM indicating that a remote function actuator unlock command was received. In response to the message and if the twilight sensor indicates night time conditions, the DIM will activate the headlamp and park lamp relay. The DIM will flash the headlights and park lights twice, then they will remain on for approximately 25 seconds or until a door is opened. When the RFA module receives a door lock command from the RFA transmitter the DIM will flash the headlights and park lights once.