Daytime Running Lamps (DRL)

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 instrument panel Integration Module (IPM) in response to changes to the outside (ambient) light level. When the IPM receives this signal, the IPM sends a class 2 message to the DIM and to the Rear Integration Module (RIM). When the headlamp switch is in AUTO, the DIM 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. The FOG/DRL fuse in the underhood fuse block supplies battery positive voltage to the switch circuit of the Daytime Running Lamp (DRL) relay. Battery positive voltage is also supplied to the DRL relay control circuit from the underhood fuse block which is energized by the DIM. When the DIM energizes the DRL relay control circuit, the current flows from the switch contacts of the DRL relay 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 G401. The high beam headlamps are now 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.