Daytime Running Lamp: Description and Operation

The daytime running lamps illuminate the high beam headlamps at a reduced intensity. The DRL will operate when all of the following conditions are present:
^ The ignition switch is in the ON position.
^ The gear selector is out of the PARK position.
^ The headlamp switch is in the OFF position.
^ The ambient light sensor indicates daytime conditions.

The BCM will not activate the Daytime Running Lamps (DRL) feature if the headlamps have already been turned on through the headlamp switch or twilight sentinel. The ambient light sensor is a variable resistor that varies its voltage signal to the Instrument Cluster (IPC) in response to changes to the outside (ambient) light level. The value of the input voltage is between 0 and 5 volts. As the ambient light decreases, the resistance of the ambient light sensor increases. When the IPC receives this signal, the IPC sends a class 2 message in order to communicate the level of ambient light to the Body Control Module (BCM). When the twilight delay switch is moved out of the OFF position, the BCM either turns on the DRL or turns on the low beam headlamps, after a timed delay depending on whether daylight or low light conditions are sensed. The time delay is normally 8 - 20 seconds, and cannot be altered or adjusted. Any function or condition that turns on the headlights will cancel the DRL operation.

The underhood fuse block provides ignition 1 voltage to the DRL relay coil through the IGN 1 fuse. The underhood fuse block also provides battery positive voltage to the DRL relay switch through the DRL fuse. When the ignition switch is in the RUN position, the ambient light sensor indicates daytime conditions, and the gear selector is not in the PARK position, a message is sent from the IPC to the BCM in order to activate the DRL. With the ignition switch in the RUN position, battery positive voltage is supplied to the DRL relay coil. When the BCM receives a message from the instrument cluster to activate the DRL, the BCM provides a ground to the DRL relay coil. The coil is then energized closing the normally open switch contacts. Battery positive voltage is then supplied through the DRL relay to the LH high beam headlamp and the RH high beam headlamp, which are in series. Ground is provided to both headlamps from G101. The LH and RH high beam headlamps will then illuminate at half intensity because they are in series.