GMC 2012 Sierra Owner's Manual page 333

Normal
Severe
Extreme
Vehicle in Tow*
*See
.
You can choose among four driving
settings:
Indicator lights in the dial show
which setting you are in. The
indicator lights will come on briefly
when you turn on the ignition and
one will stay on. If the lights do not
come on, you should take the
vehicle to your dealer for service.
An indicator light flashes while
shifting the transfer case and
remains illuminated when the shift is
complete. If for some reason the
YES
YES
YES
or
transfer case cannot make a
requested shift, it will return to the
last chosen setting.
setting is used for driving in most
street and highway situations. The
front axle is not engaged in
Two-Wheel Drive. This setting also
provides the best fuel economy.
the Four-Wheel Drive High position
when extra traction is needed, such
as on snowy or icy roads or in most
off-road situations. This setting also
engages the front axle to help drive
the vehicle. This is the best setting
to use when plowing snow.
YES
setting also engages the front axle
and delivers extra torque. You may
never need this setting. It sends
maximum power to all four wheels.
You might choose Four-Wheel Drive
Low while driving off-road in deep
sand, deep mud, deep snow, and
while climbing or descending steep
hills.
This
Use
This