GMC Sierra 2018 Owner's Manual page 264

An indicator light comes on when
four-wheel drive is engaged. See
Four-Wheel-Drive Light 0 150.
N (Neutral) : Use only when the
vehicle needs to be towed.
See Recreational Vehicle Towing
0 416 or Towing the Vehicle 0 416.
2 (Two-Wheel Drive High) : Use
this setting for driving on most
streets and highways. The front axle
is not engaged. This setting
provides the best fuel economy.
4 (Four-Wheel Drive Low) : This
setting also engages the front axle
and delivers extra torque. Choose 4
if driving off-road in deep sand,
deep mud, or deep snow, and while
climbing or descending steep hills.
When engaged, keep vehicle speed
below 72 km/h (45 mph).
4 (Four-Wheel Drive High) : Use
this setting when extra traction is
needed. The front axle engages and
helps when driving on snowy or icy
roads, when off-roading, or when
plowing snow.
The vehicle can be shifted between
2 and 4 while the vehicle is
moving. In extremely cold weather,
it may be necessary to stop or slow
the vehicle to shift into 4 .
Using the Manual Transfer Case
Use quick motions to shift into or
out of 4 or N (Neutral).
Shifting may be harder when the
vehicle is cold, but will return to
normal once warmed up.
Four-wheel drive reduces fuel
economy.
Delayed shifts from 4 to 2 may
be experienced due to uneven
tire wear, low tire pressure, high
vehicle loading, or cold
temperatures.
Shifting from 2 to 4
Shifts can be made at any
vehicle speed.
Shift in one continuous motion.
Shifting while the vehicle is in
motion may require that
moderate force be applied to the
Driving and Operating
shift lever before 4 can be
engaged, especially in cold
weather.
In extremely cold weather, it may
be necessary to slow or stop the
vehicle to shift.
While in 4 , the vehicle can be
driven at any posted legal speed
limit.
Shifting In or Out of 4
Caution
Shifting the transfer case into 4
while moving at speeds faster
than 5 km/h (3 mph) may cause
premature wear to the transfer
case, and may cause the gears to
grind.
1. If possible, shift with the
vehicle moving 5 km/h (3 mph)
or less.
2. Shift the transmission into
N (Neutral).
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