GMC 2012 Sierra Denali Owner's Manual page 427

Notice: Towing an all-wheel-drive
vehicle with all four wheels on the
ground, or even with only two of
its wheels on the ground, will
damage drivetrain components.
Do not tow an all-wheel-drive
vehicle with any of its wheels on
the ground.
All-wheel-drive vehicles are not
designed to be towed with any
wheels on the ground. If the vehicle
must be towed, see Towing the
Vehicle in this section.
Dinghy Towing
Two-Wheel-Drive Vehicles
Notice: If the vehicle is towed
with all four wheels on the
ground, the drivetrain
components could be damaged.
The repairs would not be covered
by the vehicle warranty. Do not
tow the vehicle with all four
wheels on the ground.
Two-wheel-drive vehicles should not
be towed with all four wheels on the
ground. Two-wheel-drive
Vehicle Care
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.
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