whether daylight or low light conditions are sensed. When the BCM energizes the DRL relay, the
DRL receives voltage on the DRL supply voltage circuit.
Fog Lamps
With both the ignition switch in the RUN position, and the park lamps ON, the fog lights will
illuminate when the driver depresses the fog lamp switch. The BCM receives the park lamp ON
signal from the interior park lamps supply voltage signal circuit. With the headlamp switch in
either the park or headlamp position, and the fog lamp switch is in the ON position, the BCM
will ground the fog lamp relay control circuit causing the relay to energize. The current flows
from the fog lamp relay to both front fog lamps. The state of the fog lamps will remain the same
until the fog lamp switch position is changed, or the ignition switch is cycled OFF and ON. Fog
lamp operation will be cancelled whenever the park lamps, are turned OFF or the high beam
headlights have been selected.
Park, Tail and Marker Lamps
The park, tail and marker lamps, including the license lamps, are turned on when the headlamp
switch is placed in the PARK or HEAD position or anytime the headlights are requested. The
underhood fuse block supplies battery positive voltage to both the park lamp relay switch
contacts and the park lamp coil circuit. The BCM provides a ground or control circuit to the park
lamp relay coil circuit. When the park lamps are turned ON, the BCM energizes the park lamp
relay. If the headlight switch is left in the ON position, the inadvertent power control feature will
turn OFF the park, tail and marker lamps approximately 10 minutes after the ignition switch is
turned to the OFF position. If the driver places the headlight switch in the ON position after the
ignition switch has been turned OFF, or if the ignition switch is in the ACCY position, the park,
tail and marker lamps will remain on until turned OFF or the battery runs dead.
Exterior Courtesy Lamps
The BCM, driver door switch, and the passenger door switch communicate through the GMLAN
serial data system. The driver door switch and passenger door switch supply power and ground to
the left and right exterior lamps respectively. When the BCM commands illuminated entry, a
command is also sent to the door switches for illumination of the exterior courtesy lamps. If the
door locks are activated to the LOCK position, or if the ignition switch is turned to either the ON
or RUN position the exterior courtesy lamps will deactivate immediately.
Turn Signal/Hazard Lamps
When the turn signal switch is placed in either the left or right position, a ground signal is
completed from the turn signal switch to the BCM. When the hazard flasher switch is activated, a
ground signal is completed from the turn signal/hazard switch to the BCM. The BCM then sends
2008 Chevrolet Silverado 1500
2008 ACCESSORIES & EQUIPMENT Lighting - Cab & Chassis Sierra, Cab & Chassis Silverado, Sierra & Silverado