GMC 2014 Sierra Owner's Manual page 304

This setting is ideal for use
when road surface traction
conditions are variable. When
driving the vehicle 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. Driving
in this mode results in slightly lower
fuel economy than Two-Wheel
Drive High.
this position when extra traction is
needed, such as on snowy or icy
roads or in most off-road situations.
This setting also engages the front
axle to help drive the vehicle. This is
the best setting to use when
plowing snow.
setting also engages the front axle
and delivers extra torque. You may
never need this setting. It sends
maximum power to all four wheels.
You might choose Four-Wheel Drive
Low if you are 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
.
Shifting the transfer case to
N (Neutral) can cause the vehicle
Use
to roll even if the transmission is
in P (Park). You or someone else
could be seriously injured. Be
sure to set the parking brake
before placing the transfer case in
N (Neutral). See
.
This
Shift the vehicle's
transfer case to N (Neutral) only
when towing the vehicle. See
or
.
If the SERVICE 4WD message
stays on, take the vehicle to your
dealer for service. See SERVICE
4WD under
Turn the knob to the Four-Wheel
Drive High or AUTO position. This
can be done at any speed, except
when shifting from Four-Wheel
Drive Low. The indicator light will
flash while shifting. It will remain on
when the shift is completed.
Turn the knob to the Two-Wheel
Drive High position. This can be
done at any speed, except when
shifting from Four-Wheel Drive Low.
The indicator light will flash while
shifting. It will remain on when the
shift is completed.
.