Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)

The ambient light sensor is a light sensitive transistor that varies its voltage signal to the body control module (BCM) in response to changes to the outside (ambient) light level. When the BCM receives this signal it will either turn on the low beam headlamps at a reduced intensity for daytime running lamp (DRL) operation through the DRL diode and the 2 DRL relays or the headlamps, through the low beam relay, at full intensity including all the appropriate exterior lamps, for auto headlamp operation. The low beam headlights, alone at a reduced intensity, are utilized as the DRL. Any function or condition that turns ON the headlights will cancel the DRL operation. With the headlight switch in the OFF position, the headlights will either be turned ON or OFF, after an approximate 8 second delay, depending on whether daylight or low light conditions are sensed. When the BCM provides a ground for the 2 DRL relays for DRL operation in daylight conditions, the DRL relays illuminate the low beam headlights only. The supply voltage to these relays is reduced by the DRL diode. The DRL will operate when the ignition switch is in the RUN position, the gear selector is not in the PARK position and the parking brake is released. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL mode will be activated.