GMC 2004 Sierra 1500 Pickup Owner's Manual page 134

Recommended Transfer Case Settings
Driving
2HI
Conditions
Normal YES
Variable
Severe
Extreme
Vehicle in
Tow*
*See "Recreational Vehicle Towing" in the Index for
further information.
You can choose among four driving settings:
h
(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.
2-40
Transfer Case Settings
AUTO
4HI 4LO
4WD
YES
YES
YES
AUTO 4WD: This setting is ideal for use when road
conditions are variable. When driving your vehicle
in AUTO 4WD, the front axle is engaged, but the
vehicle's power is sent to the rear wheels. When the
N
vehicle senses a loss of traction, the system will
automatically engage four-wheel drive. Driving in this
mode results in slightly lower fuel economy than 2HI.
G
(4HI): Use 4HI when you need extra traction, such
a 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
YES
plowing snow.
g
(4LO): 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-road in deep
sand, deep mud, deep snow and climbing or descending
steep hills.