Chevrolet Silverado Classic 2007 Owner's Manual page 221

Your vehicle has a light sensor located on the
top of the instrument panel in the defroster grille
that regulates when the automatic headlamps turn
on. Be sure it is not covered, or the headlamps
will come on whenever the ignition is on.
The system may also turn on the 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
detects a change in lighting lasting longer than
the delay.
If you start your vehicle in a dark garage,
the automatic headlamp system will come
on immediately. Once you leave the garage,
it will take approximately one minute for the
automatic headlamp system to change to DRL
if it is bright enough outside. During that delay,
your instrument panel cluster may not be as
bright as usual. Make sure your instrument panel
brightness control is in the full bright position.
See Instrument Panel Brightness on page 223.
To idle your vehicle with the automatic headlamp
system off, turn the control to the off position.
You may be able to turn off your Automatic
Headlamp System. See Daytime Running
Lamps (DRL) on page 220 for more information.
Your headlamps will also stay on after you exit
the vehicle. You can program this feature using
the Driver Information Center (DIC). See DIC
Vehicle Customization on page 281.
As with any vehicle, you should turn on the
regular headlamp system when needed.
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