Shifting From Two-Wheel Drive High To Four-Wheel Drive High; Shifting In Or Out Of Four-Wheel Drive Low - GMC 2012 Sierra Owner's Manual

If the transfer case shifter is in
the N (Neutral) position and you
have difficulty reaching the
selected transfer case mode,
with the engine running, shift the
transmission momentarily to
D (Drive) and then back to
N (Neutral). This will realign the
gear teeth in the transfer case
and allow you to complete the
shift.
Shifts between Two-Wheel Drive
High and Four-Wheel Drive High
can be made at any vehicle
speed.
Shift the transfer case lever in
one continuous motion into
either the Four-Wheel Drive High
or Two-Wheel Drive High
position.
Shifting from Two-Wheel Drive
High to Four-Wheel Drive High
while the vehicle is in motion
may require that moderate force
be applied to the shift lever for a
few seconds before Four-Wheel
Drive High can be engaged,
especially in cold weather.
In extremely cold weather, it may
be necessary to slow or stop the
vehicle to shift into Four-Wheel
Drive High.
While in Four-Wheel Drive High,
the vehicle can be driven at any
posted legal speed limit.
Shifting into Four-Wheel Drive
Low should be done, if possible,
with the vehicle at a slight roll,
5 km/h (3 mph) or less.