GMC 2007 Sierra - Manual (Page 160)

Shifting into Four-Wheel Drive High or
AUTO 4WD (Automatic Four-Wheel Drive)
Press and release the Four-Wheel Drive High
or AUTO 4WD switch. 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.
Shifting into Two-Wheel Drive High
Press and release the Two-Wheel Drive High
switch. This can be done at any speed, except
when shifting from Four-Wheel Drive Low.
See shifting out of Four-Wheel Drive Low later in
this section for more information.
Shifting into Four-Wheel Drive Low
Notice: Shifting the transfer case into
Four-Wheel Drive Low while moving at speeds
faster than 3 mph (5 km/h) may cause
premature wear to the transfer case, and may
cause the gears to grind. To avoid causing
premature wear, and grinding the gears, do not
shift the transfer case into Four-Wheel Drive
Low while the vehicle is moving faster
than 3 mph (5 km/h).
To shift to Four-Wheel Drive Low, the ignition
must be in RUN and the vehicle must be stopped
or moving less than 3 mph (5 km/h) with the
transmission in NEUTRAL (N). The preferred
method for shifting into Four-Wheel Drive Low
is to have your vehicle moving 1 to 2 mph
(1.6 to 3.2 km/h). Press and release the
Four-Wheel Drive Low switch. You must wait for
the Four-Wheel Drive Low indicator light to
stop flashing and remain on before shifting the
transmission into gear.
Notice: Shifting the transmission into gear
before the Four-Wheel Drive Low indicator light
has stopped flashing could damage the
transfer case. To help avoid damaging your
vehicle, always wait for the Four-Wheel
Drive Low indicator light to stop flashing
before shifting the transmission into gear.
It is typical for your vehicle to exhibit significant
engagement noise and bump when shifting
between Four-Wheel Drive Low and Four-Wheel
Drive High ranges or from NEUTRAL (N) with
the engine running.
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