GMC 2012 Sierra Denali Owner's Manual page 285

P (Park): This position locks the
rear wheels. It is the best position to
use when you start the engine
because the vehicle cannot move
easily.
When parked on a hill, especially
when the vehicle has a heavy load,
you may notice an increase in the
effort to shift out of P (Park). See
Torque Lock under Shifting Into
Park on page 9 31 for more
information.
WARNING
It is dangerous to get out of the
vehicle if the shift lever is not fully
in P (Park) with the parking brake
firmly set. The vehicle can roll.
Do not leave the vehicle when the
engine is running unless you
have to. If you have left the
engine running, the vehicle can
move suddenly. You or others
could be injured. To be sure the
vehicle will not move, even when
you are on fairly level ground,
always set the parking brake and
move the shift lever to P (Park).
See Shifting Into Park on
page 9 31. If you are pulling a
trailer, see Driving Characteristics
and Towing Tips on page 9 66.
Driving and Operating
R (Reverse): Use this gear to
back up.
Notice: Shifting to R (Reverse)
while the vehicle is moving
forward could damage the
transmission. The repairs would
not be covered by the vehicle
warranty. Shift to R (Reverse) only
after the vehicle is stopped.
To rock the vehicle back and forth to
get out of snow, ice, or sand without
damaging the transmission, see If
the Vehicle Is Stuck on page 9 15.
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