GMC 2007 Sierra - Manual (Page 223)

The DRL system will come on when the following
conditions are met:
• The ignition is on
• The exterior lamps control is in AUTO
• The light sensor determines it is daytime
When the DRL are on, only your DRL lamps will
be on. The taillamps, sidemarker, and other lamps
will not be on. The instrument panel back
lighting will not be on either.
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.
Automatic Headlamp System
When it is dark enough outside, the automatic
headlamp system will turn on the headlamps at the
normal brightness, along with the taillamps,
sidemarker, parking lamps, and the instrument
panel lights. The radio back lighting will also
be dimly lit.
To turn off the automatic headlamp system, turn
the exterior lamps switch to the off position.
Turning off the automatic headlamp system with
the headlamp switch is not available for vehicles
first sold in Canada.
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.
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