Daytime Running Lamp: Description and Operation

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the DRL control module in response to changes to the outside ambient light level. When the DRL control module receives this signal it will either turn on the Daytime Running Lamps (DRL) or the headlights for auto headlamp operation. Any function or condition that turns on the headlights will cancel the daytime running lamps operation. The daytime running lamps (DRL) illuminate the low beam headlights at a reduced intensity. With the headlight switch in the OFF position, the headlights will either be turned ON or OFF, after an approximate 30 second delay depending on whether daylight or low light conditions are sensed. The DIC/HVAC fuse and DRL fuse in the fuse block supplies battery positive voltage to DRL control module. Ground is supplied from G200. When the DRL control module receives the signal from the ambient light sensor to turn on the DRL lamps, it applies voltage to the DRL headlamp low beam supply voltage circuit. Voltage is then applied to the DRL diode. Voltage is then applied from the DRL diode to the low beam headlamps circuit. 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.