GMC Envoy Owner's Manual page 108

CAUTION:
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It can be dangerous to get out of your vehicle if
the shift lever is not fully in PARK (P) with the
parking brake firmly set. Your vehicle can roll.
Do not leave your 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 your
vehicle will not move, even when you are on
fairly level ground, always set your parking
brake and move the shift lever to PARK (P).
CAUTION:
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If you have four-wheel drive, your vehicle will
be free to roll — even if your shift lever is in
PARK (P) — if your transfer case is in
NEUTRAL. So be sure the transfer case is in a
drive gear — not in NEUTRAL. See Four-Wheel
Drive on page 2-26.
Follow the proper steps to be sure your vehicle will not
move. See Shifting Into Park (P) on page 2-31.
If you are pulling a trailer, see Towing a Trailer on
page 4-56.
2-35