GMC 2003 Sonoma Owner's Manual page 93

A (ACCESSORY): This position lets you use things like
the radio and the windshield wipers when the engine
is off. Push in the key and turn it toward you. Your
steering wheel will remain locked, just as it was before
you inserted the key.
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CAUTION:
On manual transmission vehicles, turning the
key to LOCK will lock the steering column and
result in a loss of ability to steer the vehicle.
This could cause a collision. If you need to
turn the engine off while the vehicle is moving,
turn the key only to OFF. Don't press the key
release button while the vehicle is moving.
Notice: If your key seems stuck in LOCK and you
can't turn it, be sure you are using the correct key; if
so, is it all the way in? If it is, then turn the steering
wheel left and right while you turn the key hard.
Turn the key only with your hand. Using a tool
to force it could break the key or the ignition switch.
If none of this works, then your vehicle needs
service.
B (LOCK): This position locks your ignition, steering
wheel and transmission. It's a theft-deterrent feature.
You will only be able to remove your key when the
ignition is turned to LOCK.
C (OFF): This position lets you turn off the engine but
still turn the steering wheel. Use OFF if you must
have your vehicle in motion while the engine is off (for
example, if your vehicle is being towed).
D (RUN): This is the position for driving.
E (START): This position starts your engine.
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