Daytime Running Lamp: Description and Operation

DAYTIME RUNNING LAMPS (DRL)

Pontiac GTO vehicles are equipped with the automatic headlamp control feature. With the headlamp switch in the AUTO position, the body control module (BCM) controls the function of the park and low beam of the headlamps. A daytime running lamps (DRL) function is also integrated into the lighting system which automatically illuminates the low beam headlamps at reduced intensity on the first ignition cycle when the vehicle is travelling at speed in excess of 11 km/h (7 mph) and the headlamp switch is in either the OFF or AUTO position. A running lamp dimmer assembly is incorporated into the wiring harness circuit to provide circuit resistance for lamp dimming.

With the ignition switch in START, voltage is applied to the DRL control module through the gage fuse. Operating through the low beams at 86 percent intensity of the normal output, a number of conditions must be met before the daytime running lamps system will work properly:
- The engine is running.
- The light switch is in either the OFF or the PARK lamp position.
- The ambient light sensor senses a bright light condition.

When the above conditions are met, a path to ground is provided to the coil of the DRL relay by the instrument cluster which sends a ground signal through the dimmer assembly to the ground side of the low-beam headlamps.

The following will prevent DRL operation:
- The generator is not running, a switch in the generator closes, providing a ground to the DRL control module, disabling the DRL operation.
- The light switch is in the head position.