Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)

The low beam headlamps operate at reduced intensity when in daytime running lamps (DRL) mode. The ground circuit to the switch input side of the DRL relay has a resistor in-line to reduce the intensity of the low beam headlamps for DRL operation. With RPO T 82, the body control module (BCM) receives a signal from the ambient light sensor indicating a low or high ambient (outside) light level. Without RPO T 82, when the headlamp switch is in the ON position, the headlamp switch supplies ground directly to the headlamps and to the BCM on the headlamp low or high beam signal circuit, depending on the position of the headlamp dimmer switch. The BCM uses these signals to determine if the conditions are present to illuminate the daytime running lamps.

Under the correct conditions the BCM grounds the DRL relay control circuit energizing the DRL control relay. The now closed relay supplies ground directly to the low beam headlamps and to the BCM on the headlamp low beam signal circuit. The low beam headlamps now illuminate with reduced intensity. The DRL relay is grounded at G101. Any time the headlamps or park lamps are illuminated the DRL will not illuminate.

The conditions necessary for the BCM to illuminate the DRL are as follows:
- The ignition switch is in the RUN position.
- The headlamps and park lamps are in the OFF position.
- The park brake is OFF (released).
- The BCM is receiving a high light (daytime) condition from the ambient light sensor, if equipped with RPO T 82.