GMC 2009 Envoy Denali Owner's Manual page 102

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.
CAUTION:
{
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 2-34. If you are pulling a trailer, see
Towing a Trailer on page 4-46.
2-26
CAUTION:
{
If you have four-wheel drive, the vehicle will be free
to roll — even if the shift lever is in P (Park) — if the
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 2-28. See Shifting Into
Park on page 2-34.
Make sure the shift lever is fully in P (Park) before
starting the engine. The vehicle has an automatic
transmission shift lock control system. You have to fully
apply the brake pedal, then press the shift lever
button before you can shift from P (Park) when the
ignition key is in ON/RUN. If you cannot shift out
of P (Park), ease pressure on the shift lever and push
the shift lever all the way into P (Park) as you maintain
brake application. Then press the shift lever button
and move the shift lever into another gear. See Shifting
Out of Park on page 2-36.