GMC 2006 Sierra - Manual (Page 148)

Leaving Your Vehicle With the Engine
Running (Automatic Transmission)
{ CAUTION:
It can be dangerous to leave your vehicle with
the engine running. Your vehicle could move
suddenly if the shift lever is not fully in
PARK (P) with the parking brake firmly set.
If you have four-wheel drive and your transfer
case is in NEUTRAL, your vehicle will be free to
roll, even if your shift lever is in PARK (P).
So be sure the transfer case is in a drive
gear — not in NEUTRAL.
And, if you leave the vehicle with the engine
running, it could overheat and even catch fire.
You or others could be injured. Do not leave
your vehicle with the engine running unless
you have to.
If you have to leave your vehicle with the engine running,
be sure your vehicle is in PARK (P) and the parking brake
is firmly set before you leave it. After you move the shift
lever into PARK (P), hold the regular brake pedal down.
Then, see if you can move the shift lever away from
PARK (P) without first pulling it toward you. If you can,
it means that the shift lever was not fully locked into
PARK (P).
Torque Lock (Automatic Transmission)
If you are parking on a hill and you do not shift your
transmission into PARK (P) properly, the weight of the
vehicle may put too much force on the parking pawl in the
transmission. You may find it difficult to pull the shift lever
out of PARK (P). This is called “torque lock.” To prevent
torque lock, set the parking brake and then shift into
PARK (P) properly before you leave the driver’s seat. To
find out how, see “Shifting Into PARK (P)” listed earlier in
this section.
When you are ready to drive, move the shift lever out of
PARK (P) before you release the parking brake.
If torque lock does occur, you may need to have another
vehicle push yours a little uphill to take some of the
pressure from the parking pawl in the transmission,
so you can pull the shift lever out of PARK (P).
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