GMC 1996 Sonoma Owner's Manual page 342

Steering Column Lock Check
While parked, and with the parking brake set, try to turn
the key to LOCK in each shift lever position.
With an automatic transmission, the key should turn
to
LOCK only when the shift lever is in PARK (P).
With a manual transmission, the key should
turn to LOCK only when the shift lever is in
REVERSE (R).
On vehicles with a key release button, try to turn the key
to LOCK without pressing the button. The key should
turn to
LOCK
only when you press the key button.
On all vehicles, the key should come out only in LOCK.
Parking Brake and Automatic Transmission
PARK (P) Mechanism Check
When you are doing this check, your vehicle
could begin to
move.
You or others could
be
injured and property could be damaged. Make
sure there is room in front of your vehicle in case
it begins to roll. Be ready to apply the regular
brake at once should the vehicle begin to move.
~ ~~~~
Park on a fairly steep hill, with the vehicle facing
downhill. Keeping your foot on the regular brake, set the
parking brake.
To check the parking brake: With the engine running
and transmission in NEUTRAL (N), slowly remove
foot pressure from the regular brake pedal. Do this
until the vehicle is held by the parking brake only.
To check the PARK (P) mechanism's holding ability:
Shift to PARK (P). Then release all brakes.
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