GMC 1996 Sonoma Owner's Manual page 71

Electronic Transfer Case (Option)
If your four-wheel-drive
vehicle has the electronic
transfer case, the transfer
case switches are above the
radio controls.
Use these switches to shift into and out of four-wheel
drive. You can choose among three driving settings:
2HI: This setting is for driving in most street and
highway situations.
Your
front axle
is not
engaged
in
two-wheel drive.
4HI: This setting engages your front axle to help
drive your vehicle. Use 4HI when you need extra
traction, such as on snowy or icy roads, or in most
off-road situations.
4LO: This setting also engages your front axle to give
you extra traction. You may never need 4LO. It sends
the maximum power to all four wheels. You might
choose 4LO if you were driving off-road in sand, mud,
deep snow and climbing or descending steep hills.
Indicator lights in the switches show
you
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 your vehicle in for
service. An indicator light will flash while shifting. It will
remain illuminated when the shift is completed.
Shifting from 2HI to 4HI
Press and release the 4HI switch. This can be done at
any speed, and the front
axle
will lock automatically.
Shifting from 4HI to 2HI
Press and release the
2HI
switch. This can be done at
any speed, and the front axle will unlock automatically.
Shifting from 2HI or 4HI to 4LO
To shift from 2HI or 4HI to 4L0, the vehicle must be
stopped or moving less than 3 mph (4.8 km/h) with the
transmission in NEUTRAL (N) in vehicles equipped
with an automatic transmission. The clutch pedal must
be engaged on vehicles equipped with a manual
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