GMC 2009 Sierra 1500 Crew Cab Owner's Manual page 140

Electronic Transfer Case
Use the dial to shift into and out of four-wheel drive.
Recommended Transfer Case Settings
Driving Conditions
Normal
Severe
Extreme
Vehicle in Tow*
*See Recreational Vehicle Towing on page 4-47
Towing Your Vehicle on page 4-47
2-42
The transfer case knob
is located next to the
steering column.
Transfer Case Settings
m m n
2 4 4
YES
YES
YES
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/retailer for service. An indicator light flashes while
shifting the transfer case and remains illuminated
when the shift is complete. If for some reason the
transfer case cannot make a requested shift, it will return
to the last chosen setting.
m
2 (Two-Wheel-Drive High): This 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.
m
4 (Four-Wheel-Drive High): Use the
Four-Wheel-Drive High position when extra traction
is needed, such as on snowy or icy roads or in most
N
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.
n
4 (Four-Wheel-Drive Low): This setting also engages
the front axle and delivers extra torque. You may
YES
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.