GMC Hummer H3 2008 Owner's Handbook Manual page 226

SHIFTING OUT OF P (PARK)
Your vehicle has an automatic
transmission shift lock control
system. With the engine running,
you have to fully apply the regular
brakes before you can shift out of
P (Park).
This system is designed to prevent
ignition key removal unless the
shift lever is in P (Park) and the
shift lever button is fully released.
The shift lock control system may
not operate if your vehicle has a
flat or low-voltage battery.
If the vehicle's battery is flat, jump
start the vehicle. See "Jump Start-
ing" in Section 5.
If you cannot shift out of P (Park),
ease pressure on the shift lever,
while maintaining brake applica-
tion, then push the shift lever all
the way into park. Try to shift out
of P (Park) into the gear you want.
If the problem persists, see your
dealer for service.
If you need to have your vehicle
towed, see "Towing" in Section 5
for vehicle towing information.
Section 3
Torque Lock
If you park your vehicle on a
hill, make sure to apply the park
brake first before shifting into
P (Park). Otherwise, there will be
excessive pressure on the parking
mechanism which will make it
difficult to shift out of P (Park).
Before moving, always shift out of
P (Park) then release the park
brake.
If you cannot shift out of P (Park),
you may need to have another
vehicle push yours a little up-hill.
This takes some of the pressure
from the parking mechanism in
the transmission, so you can pull
the shift lever out of P (Park).
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