wheel GMC SIERRA 1500 2012 Repair Manual

Black plate (47,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Driving and Operating 9-47
Four-Wheel Drive Low indicator
light to stop flashing and remain on
before shifting the transmission
in gear.
Notice:Shifting the transmission
into gear before the requested
mode indicator light has stopped
flashing could damage the
transfer case. To help avoid
damaging the vehicle, always wait
for the mode indicator lights to
stop flashing before shifting the
transmission into gear.
It is typical for the vehicle to exhibit
significant engagement noise
and bump when shifting between
Four-Wheel Drive Low and
Four-Wheel Drive High ranges or
from transfer case N (Neutral) with
the engine running.
If the knob is turned to the
Four-Wheel Drive Low position
when the vehicle is in gear and/or
moving more than 5 km/h (3 mph),
the Four-Wheel Drive Low indicator
light will flash for 30 seconds
and not complete the shift. After 30 seconds the transfer case
will shift to Four-Wheel Drive
High mode.
Shifting Out of Four-Wheel
Drive Low
To shift from Four-Wheel Drive
Low to Four-Wheel Drive High,
or Two-Wheel Drive High, the
vehicle must be stopped or moving
less than 5 km/h (3 mph) with the
transmission in N (Neutral) and
the ignition in ON/RUN. The
preferred method for shifting out of
Four-Wheel Drive Low is to have
the vehicle moving 1.6 to 3.2 km/h
(1 to 2 mph). Turn the knob to
the Four-Wheel Drive High or
Two-Wheel Drive High position.
You must wait for the Four-Wheel
Drive High or Two-Wheel Drive
High indicator light to stop flashing
and remain on before shifting the
transmission into gear.
Notice:
Shifting the transmission
into gear before the requested
mode indicator light has stopped
flashing could damage the
transfer case. To help avoid
damaging the vehicle, always wait
for the mode indicator lights to
stop flashing before shifting the
transmission into gear.
It is typical for the vehicle to exhibit
significant engagement noise and
bump when shifting between
Four-Wheel Drive Low and
Four-Wheel Drive High ranges or
from transfer case N (Neutral) with
the engine running.
If the knob is turned to the
Four-Wheel Drive High,
or Two-Wheel Drive High switch
position when the vehicle is
in gear and/or moving more than
5 km/h (3 mph), the Four-Wheel
Drive High, AUTO, or Two-Wheel
Drive High indicator light will flash
for 30 seconds but will not complete
the shift.

Black plate (48,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
9-48 Driving and Operating
Shifting into Neutral
To shift the transfer case to
N (Neutral) do the following:
1. Make sure the vehicle is parkedso that it will not roll.
2. Set the parking brake and press and hold the regular brake
pedal. See Parking Brake on
page 9‑54 for more information.
3. Start the vehicle or turn the ignition to ON/RUN.
4. Shift the transmission to N (Neutral).
5. Shift the transfer case to Two-Wheel Drive High.
6. Turn the transfer case dial clockwise to N (Neutral) until it
stops and hold it there until the
Neutral light starts blinking. This
will take at least 10 seconds.
Then slowly release the dial to
the four low position. The
N (Neutral) light will come on
when the transfer case shift to
N (Neutral) is complete. 7. If the engine is running, verify
that the transfer case is in
N (Neutral) by shifting the
transmission to R (Reverse) for
one second, then shift the
transmission to D (Drive) for
one second.
8. Turn the ignition to ACC/ ACCESSORY, which will turn the
engine off.
9. Place the transmission shift lever in P (Park).
10. Release the parking brake prior to moving the vehicle.
11. Turn the ignition to LOCK/OFF.
Shifting Out of Neutral
To shift the transfer case out of
N (Neutral) do the following:
1. Set the parking brake and apply the regular brake pedal.
2. Turn the ignition to ON/RUN with the engine off, and shift the
transmission to N (Neutral).
3. Turn the transfer case dial to Two-Wheel Drive High. After the transfer case has
shifted out of N (Neutral), the
N (Neutral) light will go out.
4. Release the parking brake prior to moving the vehicle.
Notice: Shifting the transmission
into gear before the requested
mode indicator light has stopped
flashing could damage the
transfer case. To help avoid
damaging the vehicle, always wait
for the mode indicator lights to
stop flashing before shifting the
transmission into gear.
5. Start the engine and shift the transmission to the desired
position.
Excessively shifting the transfer
case into or out of the different
modes may cause the transfer case
to enter the shift protection mode.
This will protect the transfer case
from possible damage and will only
allow the transfer case to respond
to one shift per 10 seconds. The
transfer case may stay in this mode
for up to three minutes.

Black plate (49,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Driving and Operating 9-49
Automatic Transfer Case
The transfer case knob is located
next to the steering column.
Use the dial to shift into and out of
Four-Wheel Drive.
You can choose among five 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 andone will stay on. If the lights do
not come on, you should take the
vehicle to your dealer for service.
An indicator light will flash while
shifting the transfer case. It will
remain 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.
2
m(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.
AUTO (Automatic Four-Wheel
Drive): This setting is ideal for
use when road surface traction
conditions are variable. When
driving the vehicle in AUTO, the
front axle is engaged, but the
vehicle's power is sent only to the front and rear wheels automatically
based on driving conditions. Driving
in this mode results in slightly lower
fuel economy than Two-Wheel
Drive High.
4
m(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
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.
4
n(Four-Wheel Drive Low): This
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 if you are driving off-road in
deep sand, deep mud, deep snow,
and while climbing or descending
steep hills.

Black plate (50,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
9-50 Driving and Operating
If the vehicle has StabiliTrak®,
shifting into Four-Wheel Drive Low
will turn Traction Control and
StabiliTrak off. See StabiliTrak
®
System on page 9‑55.
{WARNING
Shifting the transfer case to
N (Neutral) can cause the vehicle
to roll even if the transmission is
in P (Park). You or someone else
could be seriously injured. Be
sure to set the parking brake
before placing the transfer case in
N (Neutral). SeeParking Brake on
page 9‑54.
N (Neutral): Shift the vehicle's
transfer case to N (Neutral) only
when towing the vehicle. See
Recreational Vehicle Towing on
page 10‑93 orTowing the Vehicle
on page 10‑93 for more information. If the SERVICE 4 WHEEL DRIVE
message stays on, you should
take the vehicle to your dealer for
service. See
“SERVICE 4 WHEEL
DRIVE” underTransmission
Messages on page 5‑46.
Shifting Into Four-Wheel Drive
High or AUTO (Automatic
Four-Wheel Drive)
Turn the knob to the Four-Wheel
Drive High or AUTO position. This
can be done at any speed, except
when shifting from Four-Wheel
Drive Low. The indicator light will
flash while shifting. It will remain on
when the shift is completed.
Shifting Into Two-Wheel
Drive High
Turn the knob to the Two-Wheel
Drive High position. This can be
done at any speed, except when
shifting from Four-Wheel Drive Low.
The indicator light will flash while
shifting. It will remain on when the
shift is completed. Shifting Into Four-Wheel
Drive Low
When Four-Wheel Drive Low is
engaged, vehicle speed should
be kept below 72 km/h (45 mph).
Extended high-speed operation in
Four-Wheel Drive Low may damage
or shorten the life of the drivetrain.
To shift to the Four-Wheel Drive
Low position, 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). The preferred method
for shifting into Four-Wheel Drive
Low is to have the vehicle moving
1.6 to 3.2 km/h (1 to 2 mph). Turn the
knob to the Four-Wheel Drive Low
position. You must wait for the
Four-Wheel Drive Low indicator
light to stop flashing and remain on
before shifting the transmission
into gear.

Black plate (51,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Driving and Operating 9-51
Notice:Shifting the transmission
into gear before the requested
mode indicator light has stopped
flashing could damage the
transfer case. To help avoid
damaging the vehicle, always wait
for the mode indicator lights to
stop flashing before shifting the
transmission into gear.
It is typical for the vehicle to exhibit
significant engagement noise and
bump when shifting between
Four-Wheel Drive Low and
Four-Wheel Drive High ranges or
from N (Neutral) with the engine
running.
If the knob is turned to the
Four-Wheel Drive Low position
when the vehicle is in gear and/or
moving more than 5 km/h (3 mph),
the Four-Wheel Drive Low indicator
light will flash for 30 seconds
and not complete the shift. After
30 seconds the transfer case
will shift to Four-Wheel Drive
High mode. Shifting Out of Four-Wheel
Drive Low
To shift from Four-Wheel Drive Low
to Four-Wheel Drive High, AUTO or
Two-Wheel Drive High, the vehicle
must be stopped or moving less
than 5 km/h (3 mph) with the
transmission in N (Neutral) and
the ignition in ON/RUN. The
preferred method for shifting
out of Four-Wheel Drive Low
is to have the vehicle moving
1.6 to 3.2 km/h (1 to 2 mph). Turn the
knob to the Four-Wheel Drive High,
AUTO or Two-Wheel Drive High
position. You must wait for the
Four-Wheel Drive High, AUTO or
Two-Wheel Drive High indicator light
to stop flashing and remain on
before shifting the transmission
into gear.
Notice:
Shifting the transmission
into gear before the requested
mode indicator light has stopped
flashing could damage the
transfer case. To help avoid damaging the vehicle, always wait
for the mode indicator lights to
stop flashing before shifting the
transmission into gear.
It is typical for the vehicle to exhibit
significant engagement noise
and bump when shifting between
Four-Wheel Drive Low and
Four-Wheel Drive High ranges or
from N (Neutral) with the engine
running.
If the knob is turned to the
Four-Wheel Drive High, AUTO,
or Two-Wheel Drive High switch
position when the vehicle is
in gear and/or moving more than
5 km/h (3 mph), the Four-Wheel
Drive High, AUTO or Two-Wheel
Drive High indicator light will flash
for 30 seconds but will not complete
the shift.

Black plate (52,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
9-52 Driving and Operating
Shifting into Neutral
To shift the transfer case to
N (Neutral) do the following:
1. Make sure the vehicle is parkedso that it will not roll.
2. Set the parking brake and apply the regular brake pedal. See
Parking Brake on page 9‑54 for
more information.
3. Start the vehicle or turn the ignition in ON/RUN.
4. Put the transmission in N (Neutral).
5. Shift the transfer case to Two-Wheel Drive High.
6. Turn the transfer case dial clockwise to N (Neutral) until it
stops and hold it there until
the N (Neutral) light starts
blinking. This will take at least
10 seconds. Then slowly release
the dial to the four low position.
The N (Neutral) light will come
on when the transfer case shift
to N (Neutral) is complete. 7. If the engine is running, make
sure that the transfer case is in
N (Neutral) by shifting the
transmission to R (Reverse) for
one second, then shift the
transmission to D (Drive) for
one second.
8. Turn the ignition to ACC/ ACCESSORY, which will turn
the engine off.
9. Place the transmission shift lever in P (Park).
10. Release the parking brake prior to moving the vehicle.
11. Turn the ignition to LOCK/OFF.
Shifting Out of Neutral
To shift out of N (Neutral) do the
following:
1. Set the parking brake and apply the regular brake pedal.
2. Turn the ignition to ON/RUN with the engine off, and shift the
transmission to N (Neutral). 3. Turn the transfer case dial
to Two-Wheel Drive High,
Four-Wheel Drive High,
or AUTO.
After the transfer case has
shifted out of N (Neutral), the
N (Neutral) light will go out.
4. Release the parking brake prior to moving the vehicle.
Notice: Shifting the transmission
into gear before the requested
mode indicator light has stopped
flashing could damage the
transfer case. To help avoid
damaging the vehicle, always wait
for the mode indicator lights to
stop flashing before shifting the
transmission into gear.
5. Start the engine and shift the transmission to the desired
position.

Black plate (53,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Driving and Operating 9-53
Brakes
Antilock Brake
System (ABS)
This vehicle has the Antilock
Brake System (ABS), an advanced
electronic braking system that helps
prevent a braking skid.
When the engine is started and the
vehicle begins to drive away, ABS
checks itself. A momentary motor or
clicking noise might be heard while
this test is going on, and it might
even be noticed that the brake
pedal moves a little. This is normal.
If there is a problem with ABS, this
warning light stays on. SeeAntilock
Brake System (ABS) Warning Light
on page 5‑26. If driving safely on a wet road and it
becomes necessary to slam on the
brakes and continue braking to
avoid a sudden obstacle, a
computer senses that the wheels
are slowing down. If one of the
wheels is about to stop rolling, the
computer will separately work the
brakes at each wheel.
ABS can change the brake pressure
to each wheel, as required, faster
than any driver could. This can help
the driver steer around the obstacle
while braking hard.
As the brakes are applied, the
computer keeps receiving updates
on wheel speed and controls
braking pressure accordingly.
Remember: ABS does not change
the time needed to get a foot up to
the brake pedal or always decrease
stopping distance. If you get too
close to the vehicle in front of you,
there will not be enough time to
apply the brakes if that vehicle
suddenly slows or stops. Always
leave enough room up ahead to
stop, even with ABS.
Using ABS
Do not pump the brakes. Just hold
the brake pedal down firmly and let
ABS work. You might hear the ABS
pump or motor operating and feel
the brake pedal pulsate, but this is
normal.
Braking in Emergencies
ABS allows the driver to steer and
brake at the same time. In many
emergencies, steering can help
more than even the very best
braking.

Black plate (57,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Driving and Operating 9-57
It is recommended to leave the
system on for normal driving
conditions, but it may be necessary
to turn the system off if the vehicle
is stuck in sand, mud, ice or snow,
and you want to“rock”the vehicle to
attempt to free it. It may also be
necessary to turn off the system
when driving in extreme off-road
conditions where high wheel spin is
required. See If the Vehicle Is Stuck
on page 9‑15.
When the transfer case is in 4LO,
the stability system is automatically
disabled, the StabiliTrak light comes
on, and the appropriate message
will appear on the DIC. Both
traction control and StabiliTrak
are automatically disabled in this
condition.
Traction Control Operation
The TCS is part of the StabiliTrak
system. Traction control limits wheel
spin by reducing engine power
to the wheels (engine speed
management) and by applying brakes to each individual wheel
(brake-traction control) as
necessary.
The TCS is enabled automatically
when the vehicle is started. It will
activate and the StabiliTrak light
will flash if it senses that any of the
wheels are spinning or beginning to
lose traction while driving. If traction
control is turned off, only the
brake-traction control portion of
traction control will work. The
engine speed management will be
disabled. In this mode, engine
power is not reduced automatically
and the driven wheels can spin
more freely. This can cause the
brake-traction control to activate
constantly.
Notice:
If the wheel(s) of one axle
is allowed to spin excessively
while the StabiliTrak
®, ABS, brake
warning lights, and any relevant
DIC messages are displayed, the
transfer case could be damaged.
The repairs would not be covered
by the vehicle warranty. Reduce
engine power and do not spin the wheel(s) excessively while these
lights and messages are
displayed.
The TCS may activate on dry or
rough roads or under conditions
such as heavy acceleration while
turning or abrupt upshifts/downshifts
of the transmission. When this
happens, a reduction in acceleration
may be noticed, or a noise or
vibration may be heard. This is
normal.
If cruise control is being used when
the system activates, the StabiliTrak
light will flash and cruise control will
automatically disengage. Cruise
control may be reengaged when
road conditions allow. See
Cruise
Control on page 9‑58.
StabiliTrak may also turn off
automatically if it determines that a
problem exists with the system.
If the problem does not clear itself
after restarting the vehicle, see your
dealer for service.

Black plate (58,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
9-58 Driving and Operating
Non-hybrid vehicles with StabiliTrak
have a Trailer Sway Control (TSC)
feature. SeeTrailer Sway Control
(TSC) on page 9‑105.
Non-hybrid vehicles with StabiliTrak
have a Hill Start Assist (HSA)
feature. See Hill Start Assist (HSA)
on page 9‑54.
Adding non‐dealer accessories can
affect the vehicle's performance.
See Accessories and Modifications
on page 10‑3.
Locking Rear Axle
Vehicles with a locking rear axle can
give more traction on snow, mud,
ice, sand, or gravel. It works like a
standard axle most of the time, but
when traction is low, this feature will
allow the rear wheel with the most
traction to move the vehicle.
Cruise Control
{WARNING
Cruise control can be dangerous
where you cannot drive safely at
a steady speed. So, do not use
the cruise control on winding
roads or in heavy traffic.
Cruise control can be dangerous
on slippery roads. On such roads,
fast changes in tire traction can
cause excessive wheel slip, and
you could lose control. Do not use
cruise control on slippery roads.
For vehicles with cruise control, a
speed of about 40 km/h (25 mph)
or more can be maintained
without keeping your foot on the
accelerator. Cruise control does not
work at speeds below about 40 km/h
(25 mph). When the brakes are applied, cruise
control is turned off.
For vehicles with an Allison or
Hydra‐Matic 6‐speed automatic
transmission, see
“Grade Braking”
under Tow/Haul Mode on page 9‑39
for an explanation of how cruise
control interacts with the Range
Selection Mode, tow/haul and grade
braking systems.
For vehicles with the StabiliTrak
system that begins to limit wheel
spin while you are using cruise
control, the cruise control will
automatically disengage. See
StabiliTrak
®System on page 9‑55.
When road conditions allow the
cruise control to be safely used
again, it can be turned back on.

Black plate (59,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Driving and Operating 9-59
I(On/Off):Press to turn the
system on or off. The indicator light
is on when cruise control is on and
turns off when cruise control is off.
+ RES (Resume/Accelerate):
Press briefly to resume to a
previously set speed, or press and
hold to accelerate.
SET −(Set/Coast): Press to set
the speed and activate cruise
control or make the vehicle
decelerate.
[(Cancel): Press to disengage
cruise control without erasing the
set speed from memory.
Setting Cruise Control
If the cruise button is on when not in
use, it could get bumped and go into
cruise when not desired. Keep the
cruise control switch off when cruise
is not being used.
The cruise control light on the
instrument panel cluster will come
on after the cruise control has been
set to the desired speed.
1. Press
I.
2. Get up to the desired speed.
3. Press the SET− button located
on the steering wheel and
release it.
4. Take your foot off the accelerator. Resuming a Set Speed
If the cruise control is set at a
desired speed and then the brakes
are applied, the cruise control is
disengaged without erasing the set
speed from memory.
Once the vehicle speed reaches
about 40 km/h (25 mph) or more,
press the +RES button on the
steering wheel. The vehicle returns
to the previous set speed and stays
there.
Increasing Speed While Using
Cruise Control
If the cruise control system is
already activated,
.Press and hold the +RES button
on the steering wheel until the
desired speed is reached, then
release it.
.To increase vehicle speed in
small amounts, press the
+RES button. Each time this is
done, the vehicle goes about
1.6 km/h (1 mph) faster.