Tahoe 2WD V8-4.8L VIN V (2004)
Daytime Running Lamp: Description and Operation
DAYTIME RUNNING LAMPS (DRL)
The DRL will operate when the ignition switch is in the RUN position, the gear selector is not in the PARK position, and the headlamp switch is in the
AUTO position. When these conditions have been met and the ambient light sensor indicates daytime conditions, the DRL will illuminate. 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 DRL or the headlamps for auto headlamp operation. Any function or condition
that turns on the headlights will cancel the daytime running lamps operation. The DRL can be manually turned OFF by depressing the AHL/DRL switch
in the headlamp switch. The AHL/DRL defeat switch sends a ground signal through the DRL switch signal circuit to the BCM. The BCM then turns OFF
the DRL. When the AHL/DRL are manually turned OFF at the headlamp switch, the AHL/DRL will default to ON with the next ignition cycle. The DRL
are separate lamps independent of the headlamps. With the headlight switch in the AUTO position, the DRL will either be turned ON or OFF, after an
approximate 8 second delay depending on whether daylight or low light conditions are sensed. The DRL 10 A fuse in the underhood fuse block supplies
battery positive voltage to the DRL relay switch contacts and relay coil. When the BCM energizes the DRL relay , the DRL receive voltage on the DRL
supply voltage circuit. Ground for the DRL is at G100.
