Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)

The front turn signal lamps are used as both daytime running lamps (DRL) and turn signals lamps. The body control module (BCM) illuminates the front turn signals lamps in a non flashing mode for DRL operation. If the turn signal switch is activated during DRL operation, the appropriate turn signal will flash.

The DRL are designed to be automatically illuminated when the ignition is ON and the outside (ambient) light level is high as in daytime conditions (day mode). The DRL will not operate if the ambient light levels are too low (night mode). Light levels are detected by the ambient light sensor, a light sensitive transistor that varies its voltage signal to the BCM in response to changes to the ambient light level. When the BCM receives a day mode signal from the ambient light sensor it will then illuminate the DRL lamps. The automatic headlamps and park lamps will not operate when the DRL lamps are on.

In the day mode, the ambient light sensor detects daylight and the BCM applies voltage to the LH and RH front turn signal lamps illuminating the lamps under the following conditions:
- The ignition switch is in the RUN position.
- The headlamps are OFF.
- The park brake is OFF (released).
- The RH or LH turn signal is OFF.

Daytime running lamps (DRL) are controlled by the BCM based on input from the high beam headlamp circuit 1200, the low beam headlamp circuit 1201, the parking brake circuit 1134 and ignition switch state.

When DRL operation is desired, the BCM switches circuit 592 to ground. This action energizes the DRL relay. When energized, the DRL relay operates the left high beam headlamp and right high beam headlamp as a series circuit, 1/2 of battery voltage across each high beam headlamp.

When DRL operation is not desired, the BCM does not provide ground for the DRL relay. When not energized, as when high beam headlamps are desired, the DRL relay operates the right and left high beam headlamps as a parallel circuit, full battery voltage across each high beam headlamp.




For DRL operation, the parking brake must be fully released, the ignition switch must be in the RUN position and headlamp switch must be in the OFF position. Under normal operating conditions, the feedback voltage to the BCM measured at circuit 1200 is as shown in the chart.