GMC 2011 Sierra Denali Owner's Manual page 433

Two-wheel-drive vehicles should
not be towed with all four wheels
on the ground. Two-wheel-drive
transmissions have no provisions
for internal lubrication while being
towed.
Four-Wheel-Drive Vehicles
Use the following procedure to
dinghy tow a four-wheel-drive
vehicle:
1. Position the vehicle being towed
behind the tow vehicle and shift
the transmission to P (Park).
2. Turn the engine off and firmly set
the parking brake.
3. Securely attach the vehicle
being towed to the tow vehicle.
WARNING
Shifting a four-wheel-drive
vehicle's transfer case into
N (Neutral) can cause the vehicle
to roll even if the transmission is
in P (Park). The driver or others
could be injured. Make sure the
parking brake is firmly set before
the transfer case is shifted to
N (Neutral).
4. Shift the transfer case to
N (Neutral). See Shifting into
Neutral under Four-Wheel Drive
on page 9 44 for the proper
procedure to select the Neutral
position for the vehicle.
Vehicle Care
5. Release the parking brake only
after the vehicle being towed is
firmly attached to the towing
vehicle.
6. Turn the ignition to LOCK/OFF
and remove the key
steering wheel will still turn.
After towing, see Shifting Out of
Neutral under Four-Wheel Drive on
page 9 44 for the proper procedure
to take the vehicle out of the Neutral
position.
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