Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)/TWILIGHT SENTINEL

Twilight sentinel is a driver convenience that controls the exterior lamps in response to changes to the outside, ambient light level. The twilight sentinel will also keep the exterior lamps on for a pre-selected period of time after the ignition is turned to the OFF position with nighttime conditions sensed. The exterior lamps will be turned off automatically after the delay period elapses. The delay period ranges 0 seconds to 3 minutes in approximately 12 second increments. The twilight delay switch in the headlamp switch is supplied a reference voltage from the HVAC control module with C67 or instrument panel module (IPM) with CJ2. It is supplied a reference ground from the control module. The switch is a potentiometer that resistance varies as the switch is moved. The control module receives an input voltage proportional to the resistance of the potentiometer. The control module 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 an ON position, the DIM will automatically control the headlamps on/off status depending on the low light/daylight status of the sunload sensor assembly. 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 low light conditions. The sunload sensor assembly is a light sensitive photocell that varies its voltage signal to the HVAC control module or IPM in response to changes to the outside (ambient) light level. When the HVAC control module or IPM receives this signal, the HVAC control module or IPM sends a class 2 message to the DIM and to the rear integration module (RIM). When the twilight delay switch is in ON, the DIM either turns on the daytime running lamp (DRL) or turns on the low beam headlights, after a 20 second delay depending on whether daylight or low light conditions are sensed. Any function or condition that turns on the headlights will cancel the DRL operation. During DRL the low beam headlamps are on for DRL operation in daylight conditions or low beam headlamps and exterior park lamps on in low light conditions. Battery positive voltage is supplied at all times to the coil side of the DRL relay. When a daylight condition exists the DIM applies a ground to the DRL relay through the DRL relay control circuit. This energizes the DRL relay, and applies battery positive voltage from the FOG/DRL fuse through switched contacts of the DRL relay to the DRL voltage supply circuit. The DRL voltage supply circuit uses the length of the wire to reduce the voltage to the DRL lamps. The DRL supply voltage is applied to the HDLOBMR fuse which allows battery positive voltage to be applied to the HDLOBML fuse and to the left and right low beam headlamps. Ground for the left low beam headlamp is supplied from G103 and ground for the right low beam headlamp is supplied form G401.