GMC 2015 Sierra Denali Owner's Manual page 223

9-44 Driving and Operating
The settings are:
N (Neutral): Shift the vehicle's
transfer case to N (Neutral) only
when towing the vehicle. See
Recreational Vehicle Towing on
page 10-91 or Towing the Vehicle
on page 10-91.
2 (Two-Wheel Drive High): Use
for driving on most streets and
highways. The front axle is not
engaged. This setting provides the
best fuel economy.
AUTO (Automatic Four-Wheel
Drive): Use when road surface
traction conditions are variable.
When driving in AUTO, the front
axle is engaged, and the vehicle's
power is sent to the front and rear
wheels automatically based on
driving conditions. This setting
provides slightly lower fuel economy
than 2 .
Do not use AUTO mode to park on
a steep grade with poor traction
such as ice, snow, mud or gravel. In
AUTO mode only the rear wheels
will hold the vehicle from sliding
when parked. If parking on a steep
grade, use 4 to keep all four
wheels engaged.
4 (Four-Wheel Drive High): Use
this position when extra traction is
needed, such as when driving on
snowy or icy roads, off-roading,
or plowing snow.
4 (Four-Wheel Drive Low): This
setting engages the front axle and
delivers extra torque. Choose 4
when driving off-road in deep sand,
deep mud, or deep snow, and while
climbing or descending steep hills.
Shifting into Four-Wheel Drive Low
will turn Traction Control and
StabiliTrak off. See Traction Control/
Electronic Stability Control on
page 9-49.
Shifting Into 4 or AUTO
Turn the knob to the 4 or AUTO
position at any speed, except from
4 . The indicator light will flash
while shifting and will remain on
when the shift is completed.
Shifting Into 2
Turn the knob to 2 at any speed,
except when shifting from 4 . The
indicator light will flash while shifting
and will remain on when the shift is
completed.
Shifting Into 4
When 4 is engaged, keep vehicle
speed below 72 km/h (45 mph).
To shift to 4 :
1. The ignition must be in ON/RUN
and the vehicle must be stopped
or moving less than 5 km/h
(3 mph) with the transmission in
N (Neutral). It is best for the
vehicle to be moving
1.6 to 3.2 km/h (1 to 2 mph).