GMC 2001 Yukon XL Owner's Manual page 103

Automatic Transfer Case (If Equipped)
Use these switches to shift into and out of
-
four wheel drive.
The transfer case switches
are located to the left of the
instrument panel cluster.
You can choose among four driving settings:
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.
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 only to the rear wheels. When the 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.
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