2006 GMC SIERRA 1500 automatic transmission

4n(Four-Wheel Low):This setting also engages
your front axle to give you extra traction. You may never
need Four-Wheel Low. It sends the maximum power to all
four wheels. You might choose Four-Wheel Low if you
were driving off-road in sand, mud or deep snow and
while climbing or descending steep hills. When operating
in Four-Wheel Low, the gear ratio provides additional
torque when compared to Four-Wheel High. The
transmission gear shift feel will be exaggerated.
Indicator lights in the switches show you which setting
you are in. The indicator lights will come on briey when
you turn on the ignition and the last chosen setting will
stay on. If the lights do not come on, you should take your
vehicle in for service. An indicator light will ash while
shifting. Fast ashing means the conditions were not met
to make the desired shift, typically the vehicle was going
too fast, the automatic transmission was not in neutral,
or the clutch pedal was not fully pressed. Slow ashing
means the shift is in progress. It will stay on when the
shift is completed. If for some reason the transfer cannot
make a requested shift, it will return to the last chosen
setting.Shifting from Two-Wheel High to
Four-Wheel High
Press and release the Four-Wheel High switch. This
can be done at any speed, and the front axle will lock
automatically with some delay.
Shifting from Four-Wheel High to
Two-Wheel High
Press and release the Two-Wheel High switch. This
can be done at any speed, and the front axle will unlock
automatically with some delay.
It is normal to hear and feel your vehicle’s transfer case
shift into Four-Wheel Low. If you shift with the vehicle
stopped, the indicator light may remain ashing slowly.
It may be necessary to shift the transmission momentarily
into REVERSE (R) and DRIVE (D), for an automatic
transmission, or REVERSE (R) and FIRST (1) for a
manual transmission to have the light stop ashing.
2-48

Shifting from Two-Wheel High or
Four-Wheel High to Four-Wheel Low
Notice:Shifting the transfer case into
Four-Wheel Low while moving at speeds faster
than 3 mph (5 km/h) may cause premature wear to
the transfer case, and may cause the gears to grind.
To avoid causing premature wear, and grinding the
gears, do not shift the transfer case into Four-Wheel
Low while the vehicle is moving faster than
3 mph (5 km/h).
To shift from Two-Wheel High or Four-Wheel High
to Four-Wheel Low, the vehicle must be stopped or
moving less than 3 mph (5 km/h) with the transmission in
NEUTRAL (N) for an automatic transmission or the clutch
pedal pressed for a manual transmission. The preferred
method for shifting into four-wheel low is to have your
vehicle moving 3 mph (5 km/h).Press and release the Four-Wheel Low switch. You
must wait for the four-wheel low indicator light to stop
ashing and stay on before shifting your transmission
into gear or releasing the clutch pedal.
Notice:Shifting the transmission into gear before
the Four-Wheel Low indicator light has stopped
ashing could damage the transfer case. To help
avoid damaging your vehicle, always wait for the
Four-Wheel Low indicator light to stop ashing
before shifting the transmission into gear.
If the Four-Wheel Low switch is pressed when your
vehicle is in gear and/or moving, the Four-Wheel Low
indicator light will ash for 30 seconds and not complete
the shift unless your vehicle is moving slower than
3 mph (5 km/h) and the transmission is in NEUTRAL (N).
The transfer case will shift to Four-Wheel High while
waiting to complete the shift.
2-49

Shifting from Four-Wheel Low to
Four-Wheel High or Two-Wheel High
To shift from four-wheel low to Four-Wheel High or
Two-Wheel High, your vehicle must be stopped or
moving less than 3 mph (5 km/h) with the transmission in
NEUTRAL (N) for an automatic transmission or the clutch
pedal pressed for a manual transmission. The preferred
method for shifting out of Four-Wheel Low is to have your
vehicle moving 3 mph (5 km/h).
Press and release the Two-Wheel High or Four-Wheel
High switch. You must wait for the Two-Wheel High or
Four-Wheel High indicator light to stop ashing and
remain on before shifting your transmission into gear
or releasing the clutch pedal.
If the Four-Wheel High switch is pressed when your
vehicle is in gear and/or moving, the Four-Wheel High
indicator light will ash for 30 seconds but will not
complete the shift unless the vehicle is moving slower
than 3 mph (5 km/h) and the transmission is in
NEUTRAL (N).
Shifting into NEUTRAL
{CAUTION:
Shifting the transfer case to NEUTRAL
can cause your vehicle to roll even if the
transmission is in PARK (P). You or someone
else could be seriously injured. Be sure to set
the parking brake before placing the transfer
case in NEUTRAL. SeeParking Brake on
page 2-52.
To shift the transfer case to NEUTRAL, rst make sure
the vehicle is parked so that it will not roll:
1. Set the parking brake.
2. Start the vehicle or turn the ignition to RUN.
3. Press the foot brake pedal and put the transmission
in NEUTRAL (N).
2-50

4. Shift the transfer case to Two-Wheel High.
5. Simultaneously press and hold the Two-Wheel High
and Four-Wheel Low buttons for 10 seconds. The
red NEUTRAL light will come on when the transfer
case shift to NEUTRAL is complete.
6. Start the engine if it is not already running.
7. Press and hold the foot brake pedal and Shift the
transmission to REVERSE (R) for one second, then
shift the transmission for one second to DRIVE (D)
for an automatic transmission, or FIRST (1) for
vehicles equipped with a manual transmission and
then let out the clutch. This is to ensure the transfer
case is in NEUTRAL. If not, repeat this procedure
starting at Step 3.
8. Turn the engine off, by turning the key to
ACCESSORY.
9. Place the transmission shift lever in PARK (P)
for an automatic transmission, or FIRST (1) for
vehicles equipped with a manual transmission.
10. Turn the ignition to LOCK.Shifting Out of NEUTRAL
To shift out of NEUTRAL:
1. Set the parking brake and press and hold the
regular brake pedal.
2. Shift the transmission to NEUTRAL (N) for an
automatic transmission, or press the clutch pedal
for vehicles equipped with a manual transmission.
Then turn the ignition to RUN with the engine off.
3. Press the button for the desired transfer case shift
position (Two-Wheel High, Four-Wheel High, or
Four-Wheel Low).
4. After the transfer case has shifted out of NEUTRAL
the red light will go out.
5. Release the parking brake.
6. You may 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.
7. After the transfer case has shifted out of NEUTRAL
the red light will go out.
2-51

Shifting Into Park (P)
(Automatic Transmission)
{CAUTION:
It can be dangerous to get out of your vehicle if
the shift lever is not fully in PARK (P) with the
parking brake rmly set. Your vehicle can roll.
If you have left the engine running, the vehicle
can move suddenly. You or others could be
injured. To be sure your vehicle will not move,
even when you are on fairly level ground, use
the steps that follow. With four-wheel drive, if
your transfer case is in NEUTRAL, your vehicle
will be free to roll, even if your shift lever is in
PARK (P). So, be sure the transfer case is in a
drive gear — not in NEUTRAL. If you are pulling
a trailer, seeTowing a Trailer on page 4-67.1. Hold the brake pedal down with your right foot and
set the parking brake.
2. Move the shift lever into the PARK (P) position by
pulling the shift lever toward you and moving it up
as far as it will go.
3. If your vehicle has four-wheel drive, be sure
the transfer case is in a drive gear – not in
NEUTRAL (N).
4. Turn the ignition key to LOCK.
5. Remove the key and take it with you. If you can
leave your vehicle with the ignition key in your
hand, your vehicle is in PARK (P).
2-53

Leaving Your Vehicle With the Engine
Running (Automatic Transmission)
{CAUTION:
It can be dangerous to leave your vehicle with
the engine running. Your vehicle could move
suddenly if the shift lever is not fully in
PARK (P) with the parking brake rmly set.
If you have four-wheel drive and your transfer
case is in NEUTRAL, your vehicle will be free to
roll, even if your shift lever is in PARK (P).
So be sure the transfer case is in a drive
gear — not in NEUTRAL.
And, if you leave the vehicle with the engine
running, it could overheat and even catch re.
You or others could be injured. Do not leave
your vehicle with the engine running unless
you have to.If you have to leave your vehicle with the engine running,
be sure your vehicle is in PARK (P) and the parking brake
is rmly set before you leave it. After you move the shift
lever into PARK (P), hold the regular brake pedal down.
Then, see if you can move the shift lever away from
PARK (P) without rst pulling it toward you. If you can,
it means that the shift lever was not fully locked into
PARK (P).
Torque Lock (Automatic Transmission)
If you are parking on a hill and you do not shift your
transmission into PARK (P) properly, the weight of the
vehicle may put too much force on the parking pawl in the
transmission. You may nd it difficult to pull the shift lever
out of PARK (P). This is called “torque lock.” To prevent
torque lock, set the parking brake and then shift into
PARK (P) properly before you leave the driver’s seat. To
nd out how, see “Shifting Into PARK (P)” listed earlier in
this section.
When you are ready to drive, move the shift lever out of
PARK (P) before you release the parking brake.
If torque lock does occur, you may need to have another
vehicle push yours a little uphill to take some of the
pressure from the parking pawl in the transmission,
so you can pull the shift lever out of PARK (P).
2-54

Shifting Out of Park (P)
(Automatic Transmission)
Your vehicle has an automatic transmission shift lock
control system which locks the shift lever in PARK (P)
when the ignition is in the LOCK position. You have to
fully apply your regular brakes before you can shift from
PARK (P) when the ignition is in RUN. SeeAutomatic
Transmission Operation on page 2-26and “Torque Lock”
underShifting Out of Park (P) (Automatic Transmission)
on page 2-55.
If your vehicle has an Allison Transmission
®, the
transmission is equipped with a park pawl designed to
hold the higher weight of commercial medium duty trucks.
Therefore, the Allison Transmission
®uses larger parts
than other automatic transmissions. These larger parts
may sometimes make a clunk noise when the selector
lever is moved from DRIVE (D) or REVERSE (R) to
PARK (P). This is normal and there is no damage
occurring during these shifts.If you cannot shift out of PARK (P), ease pressure on
the shift lever and push the shift lever all the way up into
PARK (P) as you maintain brake application. Then, move
the shift lever into the gear you want.
If you ever hold the brake pedal down but still can’t shift
out of PARK (P), try this:
1. Turn the key to ACCESSORY. There is no shift
interlock in this key position.
2. Apply and hold the brake until the end of Step 4.
3. Shift the transmission to NEUTRAL (N).
4. Start the vehicle and then shift to the gear you want.
5. Have the system xed as soon as you can.
2-55

Running the Engine While Parked
It is better not to park with the engine running. But if you
ever have to, here are some things to know.
{CAUTION:
Idling the engine with the climate control
system off could allow dangerous exhaust into
your vehicle. See the earlier caution under
Engine Exhaust on page 2-57.
Also, idling in a closed-in place can let deadly
carbon monoxide (CO) into your vehicle even if
the climate control fan is at the highest setting.
One place this can happen is a garage.
Exhaust — with CO — can come in easily.
NEVER park in a garage with the engine
running.
Another closed-in place can be a blizzard.
SeeWinter Driving on page 4-42.
{CAUTION:
It can be dangerous to get out of your vehicle
if the automatic transmission shift lever is not
fully in PARK (P) with the parking brake rmly
set. Your vehicle can roll. Do not leave your
vehicle when the engine is running unless you
have to. If you have left the engine running,
the vehicle can move suddenly. You or others
could be injured. To be sure your vehicle will
not move, even when it is on fairly level
ground, always set the parking brake and
move the automatic transmission shift lever
to PARK (P), or the manual transmission shift
lever to NEUTRAL.
2-58