GMC 2015 Sierra Owner's Manual page 306

4 (Four-Wheel Drive High): Use
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 from 2
to 4 while the vehicle is moving.
Shifting Into 4
Turn the knob to 4 at any speed
up to 121 km/h (75 mph), except
from 4 . The indicator light will flash
while shifting and will remain on the
selected setting.
Shifting Into 2
Turn the knob to 2 at any speed,
except when shifting from 4 .
Shifting Into 4
When 4 is engaged, vehicle speed
should be kept below 72 km/h
(45 mph).
1. The ignition must be in ON/RUN
and the vehicle must be stopped
or moving less than 5 km/h
(3 mph) with the transmission in
N (Neutral). It is best for the
vehicle to be moving
1.6 to 3.2 km/h (1 to 2 mph).
2. Turn the knob to 4 . Wait for the
4 indicator light to stop flashing
before shifting the transmission
into gear.
If the transmission is in gear and/or
moving more than 5 km/h (3 mph),
the 4 indicator light will flash for
30 seconds and not complete the
shift. After 30 seconds the transfer
case will shift to 4 . Turn the knob
to 4 to see the indicator. With the
vehicle moving less than 5 km/h
(3 mph), and the transmission in
N (Neutral), attempt the shift again.
Shifting Out of 4
1. To shift out of 4 the vehicle
must be stopped or moving less
than 5 km/h (3 mph) with the
Driving and Operating
transmission in N (Neutral) and
the ignition in ON/RUN. It is best
for the vehicle to be moving
1.6 to 3.2 km/h (1 to 2 mph).
2. Turn the knob to 4 or 2 . Wait
for the 4 or 2 indicator light to
stop flashing before shifting the
transmission into gear.
If the transmission is in gear and/or
moving more than 5 km/h (3 mph),
the 4 or 2 indicator light will flash
for 30 seconds, but will not complete
the shift. With the vehicle moving
less than 5 km/h (3 mph), and the
transmission in N (Neutral), attempt
the shift again.
Shifting Into N (Neutral)
To shift:
1. Park the vehicle on a level
surface.
2. Set the parking brake and press
and hold the brake pedal. See
Parking Brake on page 9-48.
3. Start the vehicle or turn the
ignition to ON/RUN.
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