GMC Sierra Classic 2007 Owner's Manual page 154

2H (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.
4H (Four-Wheel Drive High): Use this setting
when you need extra traction, such as on snowy or
icy roads or in most off-road situations. This
setting also engages the front axle to help drive
your vehicle. This is the best setting to use
when plowing snow.
You can shift from 2H to 4H or 4H to 2H while the
vehicle is moving. The front axle will engage
faster if you take your foot off of the accelerator
for a couple of seconds after you shift. In
extremely cold weather, it may be necessary to
stop or slow the vehicle to shift into 4H.
154
When Using the Manual Transfer Case
•
Shifting should be made using quick
motions. Shifting slowly may make it
more difficult to shift.
•
You may notice that it is harder to shift when
the vehicle is cold. After the vehicle warms
up the shifting will return to normal.
•
While in 4H or 4L you may experience
reduced fuel economy.
•
Avoid driving in four-wheel drive on clean, dry
pavement. Doing this may cause the tires to
wear faster, and make your transfer case
harder to shift, and run noisier.