Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL) AND TWILIGHT SENTINEL

Twilight sentinel is a driver convenience that controls the exterior lamps in response to changes to the outside, ambient light level. The ambient light sensor is a light sensitive transistor that varies its voltage signal to the lamp control module (LCM) in response to changes to the outside, ambient light level. When the twilight switch is in ON, the LCM either turns on the 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. Battery positive voltage is supplied to the left high beam ground circuit from the LCM. When the LCM energizes the left high beam ground circuit, the current flows from the LCM switch to the left high beam. After the left high beam, the current flows through the left high beam fuse and through the right high beam fuse. The current continues through the right high beam to ground G105. Now, the high beam headlamps are in series, and split the voltage. The headlamps illuminate at half intensity. The DRL operate when the ignition switch is in the RUN position, and the parking brake is not set or the transmission is not in park. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate.