GMC 1993 Suburban Owner's Manual page 76

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.
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 pushed).
Run: This is the position for driving.
Start: This starts your engine.
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 move
the key release lever while the vehicle is moving.
If
your
key seems stuck in LQCK and you can't turn it, be sure
it
is all
the way
in.
If
it
is, then turn the steering wheel
left
and
right while
you
turn
the
key hard.
But
turn the key
only
with
your
hand. Using a
tool
to
force it could break the
key or the
ignition switch.
It: none
of
this works,
then your
vehicle needs
service.
2-1
2