Chevrolet 2007 TrailBlazer Owner's Manua page 128

Leaving Your Vehicle With the Engine
Running
CAUTION:
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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, your vehicle
will be free to roll – even if your lever is in
PARK (P) – if your transfer case is in
NEUTRAL. So be sure the transfer case
is in a drive gear – not NEUTRAL.
See Four-Wheel Drive on page 121.
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.
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If you have to leave your vehicle with the engine
running, be sure your vehicle is in PARK (P)
and your parking brake is firmly set before you
leave it. After you have moved 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 pressing the
button on the console shift lever. If you can,
it means that the shift lever was not fully locked
into PARK (P).
Torque Lock
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) on page 127.