GMC 2008 Acadia - Manual (Page 108)

Ignition Positions
With the key in the ignition,
you can turn it to four
different positions.
In order to shift out of PARK (P), ignition must be in
ON/RUN or ACC/ACCESSORY and the regular brake
pedal must be applied.
Notice: Using a tool to force the key from the
ignition switch could cause damage or break the key.
Use the correct key and turn the key only with your
hand. Make sure the key is all the way in. If none of
this works, then your vehicle needs service.
A (LOCK/OFF): This is the only position in which you
can remove the key. This position locks the ignition and
transmission. If the steering wheel is locked, move it from
right to left and turn the key to ACC/ACCESSORY. If
none of this works, then your vehicle needs service.
B (ACC/ACCESSORY): This position allows you to use
things like the radio and the windshield wipers while
the engine is off. This position will also allow you to turn
off the engine.
C (ON/RUN): This is the position that the switch returns
to after you start your engine and release the key.
The switch stays in ON/RUN when the engine is
running. But even when the engine is not running, you
can use ON/RUN to operate your electrical power
accessories, and to display some instrument panel
warning lights.
The battery could be drained if you leave the key in the
ACC/ACCESSORY or ON/RUN position with the
engine off. You may not be able to start your vehicle if
the battery is allowed to drain for an extended period
of time.
D (START): This position starts the engine. When the
engine starts, release the key. The ignition switch
will return to ON/RUN for normal driving.
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