GMC 2001 Sierra 1500 Pickup Owner's Manual page 118

An indicator on the bezel near the lever shows you the
transfer case settings:
-
2 Wheel High (2HI): This setting is used for driving
in most street and highway situations. Your front axle
-
is not engaged in two wheel drive. This setting also
provides the best fuel economy.
-
4 Wheel High (4HI): Use 4HI when you need extra
traction, such as on snowy or icy roads or in most
-
off road situations. This setting also engages your front
axle to help drive your vehicle. This is the best setting to
use when plowing snow.
CAUTION:
Shifting the transfer case to NEUTRAL can
cause your vehicle to roll even if the transmission
is in PARK (P), or if you have a manual
transmission, even if you are in gear. You or
someone else could be seriously injured. Be sure
to set the parking brake before placing the
transfer case in NEUTRAL. See "Parking Brake"
in the Index.
NEUTRAL (N): Shift to this setting only when your
vehicle needs to be towed. The ignition switch must be
in RUN in order to shift the lever into NEUTRAL (N).
See "Recreational Vehicle Towing" or "Towing your
Vehicle" in the Index.
-
4 Wheel Low (4L0): This setting also engages your
front axle and delivers extra torque. You may never need
4LO. It sends maximum power to all four wheels. You
might choose 4LO if you are driving off
sand, deep mud, deep snow and climbing or descending
steep hills.
-
road in deep
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