GMC 2005 Sierra 1500 Pickup, Owner'S Manual, Page: 181 / 574

When it begins to get dark, the automatic headlamp
system will switch from DRL to the headlamps.
When you turn the headlamp switch off, the headlamps
will go off, and your DRL lamps will illuminate,
provided it is not dark outside.
Shifting the transmission into PARK (P) will allow you to
idle the vehicle with the DRL off. The DRL will stay
off until you shift the transmission out of PARK (P).
This procedure applies only to vehicles first sold in the
United States.
Automatic Headlamp System
When it is dark enough outside, your automatic
headlamp system will turn on your headlamps at the
normal brightness along with other lamps such as
the taillamps, sidemarker, parking lamps and the
instrument panel lights. The radio lights will also be dim.
To turn off the automatic headlamp system, turn the
exterior lamps switch to the off position and then
release. Turning off the automatic headlamp system
with the headlamp switch is not available for vehicles
first sold in Canada. For vehicles first sold in Canada,
you can turn off the automatic headlamp system
when parked at night by applying the parking brake
before starting your vehicle. The headlamps will remain
off once the vehicle is started for as long as you are
parked. If you release the parking brake, the lights will
turn on. If the parking brake is not released before
you begin to drive, the exterior lamps will turn on above
2 mph (3.2 km/h).
Your vehicle is equipped with a light sensor located on
the top of the instrument panel in the defroster grille.
Be sure it is not covered, or the system will be on
whenever the ignition is on.
The system may also turn on your headlamps when
driving through a parking garage, heavy overcast
weather or a tunnel. This is normal.
There is a delay in the transition between the daytime
and nighttime operation of the Daytime Running
Lamps (DRL) and the automatic headlamp systems so
that driving under bridges or bright overhead street
lights does not affect the system. The DRL and
automatic headlamp system will only be affected when
the light sensor sees a change in lighting lasting
longer than the delay.
3-15