GMC Sierra Classic 2007 Owner's Manual page 159

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.
If the Four-Wheel Drive Low switch is pressed
when your vehicle is in gear and/or moving,
the Four-Wheel Drive Low indicator light will flash
for 30 seconds and the vehicle will not complete
the shift unless it is moving less than 3 mph
(5 km/h) and the transmission is in NEUTRAL (N).
After 30 seconds the transfer case will shift to
Four-Wheel Drive High mode.
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