2007 GMC SIERRA CLASSIC automatic transmission

3. Plug it into a normal, grounded 110-volt AC
outlet.
{CAUTION:
Plugging the cord into an ungrounded
outlet could cause an electrical shock.
Also, the wrong kind of extension cord
could overheat and cause a re. You
could be seriously injured. Plug the cord
into a properly grounded three-prong
110-volt AC outlet. If the cord will not
reach, use a heavy-duty three-prong
extension cord rated for at least 15 amps.
4. Before starting the engine, be sure to unplug
and store the cord as it was before to keep it
away from moving engine parts. If you do
not, it could be damaged.
How long should you keep the coolant heater
plugged in? The answer depends on the outside
temperature, the kind of oil you have, and
some other things. Instead of trying to list
everything here, we ask that you contact yourdealer in the area where you will be parking your
vehicle. The dealer can give you the best
advice for that particular area.
Automatic Transmission Operation
If your vehicle has an automatic transmission,
it features an electronic shift position indicator
within the instrument panel cluster. This display
must be powered anytime the shift lever is moved
out of PARK (P). SeeFuses and Circuit Breakers
on page 600.
There are several different positions for your shift
lever.
Automatic Transmission
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See “Range Selection Mode” later in this section.
PARK (P):This position locks your rear wheels. It
is the best position to use when you start your
engine because your vehicle cannot move easily. If
your vehicle has the Allison Transmission
®, with the
Power Take-Off (PTO), use PARK (P) when
starting. The Allison Transmission
®has a park pawl
that is designed to hold the weight of commercial
medium duty trucks. Therefore, the Allison
Transmission
®uses larger parts than other
automatic transmissions. These larger parts may
sometimes make a clunking 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.
When parked on a hill, especially with a heavy load,you may notice an increase in the effort to shift out
of Park. See Torque Lock (Automatic Transmission)
underShifting Into Park (P) (Automatic
Transmission) on page 170for more information.
{CAUTION:
It is 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.
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 you are on fairly level
ground, always set your parking brake
and move the shift lever to PARK (P).
SeeShifting Into Park (P) (Automatic
Transmission) on page 170. If you are
pulling a trailer, seeTowing a Trailer on
page 429.
Allison Transmission®
141

{CAUTION:
If you have four-wheel drive, your vehicle
will be free to roll — even if your shift
lever is in PARK (P) — if your transfer
case is in NEUTRAL. So, be sure the
transfer case is in a drive gear, two-wheel
high (2H) or four-wheel high (4H) or
four-wheel low (4L) — not in NEUTRAL.
SeeShifting Into Park (P) (Automatic
Transmission) on page 170.
REVERSE (R):Use this gear to back up. If your
vehicle has the Allison Transmission
®,theRonthe
shift display, may blink if the shift inhibitor is active.
Notice:Shifting to REVERSE (R) while your
vehicle is moving forward could damage the
transmission. The repairs would not be covered
by your warranty. Shift to REVERSE (R) only
after your vehicle is stopped.
To rock your vehicle back and forth to get out of
snow, ice, or sand without damaging your
transmission, seeIf Your Vehicle is Stuck in Sand,
Mud, Ice, or Snow on page 406.NEUTRAL (N):In this position, your engine does
not connect with the wheels. To restart when
you are already moving, use NEUTRAL (N) only.
Also, use NEUTRAL (N) when your vehicle is
being towed.
{CAUTION:
Shifting into a drive gear while your
engine is running at high speed is
dangerous. Unless your foot is rmly on
the brake pedal, your vehicle could move
very rapidly. You could lose control and
hit people or objects. Do not shift into a
drive gear while your engine is running at
high speed.
Notice:Shifting out of PARK (P) or
NEUTRAL (N) with the engine running at high
speed may damage the transmission. The
repairs would not be covered by your warranty.
Be sure the engine is not running at high
speed when shifting your vehicle.
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DRIVE (D):This position is for normal driving. It
provides the best fuel economy for your vehicle. If
you need more power for passing, and you are:
Going less than about 35 mph (55 km/h), push
your accelerator pedal about halfway down.
Going about 35 mph (55 km/h) or more, push
the accelerator all the way down.
By doing this, the vehicle shifts down to the
next gear and has more power.
Downshifting the transmission in slippery road
conditions could result in skidding, see “Skidding”
underLoss of Control on page 371
DRIVE (D) can be used when towing a trailer,
carrying a heavy load, driving on steep hills, or for
off-road driving. You may want to shift the
transmission to THIRD (3) or, if necessary, a lower
gear selection if the transmission shifts too often.
If your vehicle has the Allison Transmission
®, it will
shift into rst range when DRIVE (D) is selected.
As vehicle speed increases, the transmission
will upshift automatically through each available
range up to SIXTH (6). As the vehicle slows,
the transmission will downshift automatically.The Allison Transmission
®uses a shift stabilization
feature that adjusts the transmission shifting to
the current driving conditions in order to reduce
rapid upshifts and downshifts. This shift
stabilization feature is designed to determine
before making an upshift if the engine will be able
to maintain vehicle speed by analyzing things
such as throttle position, vehicle load, and
hill grade. If the shift stabilization feature
determines that current vehicle speed cannot be
maintained, the transmission does not upshift
and instead holds the current gear. In some cases,
this may appear to be a delayed shift, however
the transmission is operating normally.
The Allison Transmission
®also uses adaptive shift
controls. Adaptive shift controls continually
compares key shift parameters to pre-programmed
ideal shift conditions. The Allison Transmission
®
constantly makes adjustments to improve vehicle
performance according to the way the vehicle is
being used, such as with a heavy load. During this
adaptive shift controls process, some shifts may
feel different as the transmission determines
optimum settings for a particular shift.
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MANUAL MODE (M):This position, is available
on vehicles with the Allison Transmission®.It
lets drivers select the range of gears appropriate
for current driving conditions. If your vehicle
has this feature, see Range Select Mode (Allison
Transmission
®) later in this section.
THIRD (3):This position is also used for normal
driving. However, it reduces vehicle speed
more than DRIVE (D) without using your brakes.
You might choose THIRD (3) instead of DRIVE (D)
when driving on hilly, winding roads, when
towing a trailer, so there is less shifting between
gears and when going down a steep hill.
SECOND (2):This position reduces vehicle speed
even more than THIRD (3) without using your
brakes. You can use SECOND (2) on hills. It can
help control your speed as you go down steep
mountain roads, but then you would also want to
use your brakes off and on.
If you manually select SECOND (2) in an
automatic transmission, the transmission will start
in second gear. You can use this feature for
reducing the speed of the rear wheels when you
are trying to start your vehicle from a stop on
slippery road surfaces.For an Allison Transmission
®, see Low Traction
Mode later in this section.
FIRST (1):For an automatic transmission, this
position reduces vehicle speed even more than
SECOND (2) without using your brakes. You can
use it on very steep hills, or in deep snow or mud. If
the shift lever is put in FIRST (1) while the vehicle is
moving forward, the transmission will not shift into
rst gear until the vehicle is going slowly enough.
For an Allison Transmission
®, This position reduces
vehicle speed, without using your brakes. You can
use it for major/sever downgrades and off-road
driving where the vehicle would otherwise
accelerate due to steepness of grade. When you
shift to FIRST (1) it will provide the lowest gear
appropriate to your current road speed and will
continue to downshift as the vehicle slows,
eventually downshifting to FIRST (1) gear.
Notice:Spinning the tires or holding the
vehicle in one place on a hill using only the
accelerator pedal may damage the
transmission. The repair will not be covered by
your warranty. If you are stuck, do not spin
the tires. When stopping on a hill, use the
brakes to hold the vehicle in place.
144

Low Traction Mode
(Allison Transmission®)
If your vehicle has the DURAMAX®diesel engine
and the Allison Transmission®,ithasaLow
Traction Mode that assists in vehicle acceleration
when road conditions are slippery, such as
with ice or snow. While at a stop, selecting the
second gear range using the Range Selection
system, will allow the Allison Transmission
®to limit
torque to the wheels after it detects wheel slip,
preventing the tires from spinning.
Notice:Spinning the tires or holding the
vehicle in one place on a hill using only the
accelerator pedal may damage the
transmission. The repair will not be covered by
your warranty. If you are stuck, do not spin
the tires. When stopping on a hill, use the
brakes to hold the vehicle in place.
Cold Weather Operation
(Allison Transmission®)
On cold days, approximately 32°F (0°C) or colder,
your automatic transmission is designed to shift
differently. The transmission uses a warm-up mode
shift schedule until the engine reaches normal
operating temperature. While the transmission is
in warm-up mode it is normal for transmission
upshifts to be delayed or held longer. This feature
improves heater performance by giving quicker
vehicle warm-ups.
When temperatures are below−13°F (−25°C), the
transmission will prevent certain operations to
protect against damage. When active the DIC will
display the message “Trans in Warm-up”.
SeeDIC Warnings and Messages on page 270for
more information.
146

Tow/Haul Mode
If your vehicle has an automatic transmission, it
may have a Tow/Haul mode. If your vehicle has an
Allison Transmission
®see “Tow/Haul Mode
(Allison Transmission®) following. Tow/Haul mode
adjusts the transmission shift pattern to reduce
shift cycling, providing increased performance,
vehicle control, and transmission cooling
when towing or hauling heavy loads.The selector button is located on the end of the
shift lever. Turn the Tow/Haul on and off by
pressing the button. When the Tow/Haul is on, a
light on the instrument panel cluster will come on.
SeeTow/Haul Mode Light on page 264for
more information.
If your vehicle has the Performance
Package-Enhanced Towing, activating the manual
selectable ride will adjust the shock absorber
characteristics to enhance the ride and handling of
the vehicle for towing or hauling heavy loads.
Also see Tow Haul Mode underTowing a Trailer
on page 429for more information.
147

Tow/Haul Mode (Allison
Transmission®)
If your vehicle has an Allison Transmission®,it
may have a Tow/Haul mode. Tow/Haul mode
adjusts the transmission shift pattern to reduce
shift cycling, providing increased performance,
vehicle control, and transmission cooling
when towing or hauling heavy loads.The selector button is located on the end of the shift
lever. Turn the Tow/Haul on and off by pressing the
button. When the Tow/Haul is on, a light on the
instrument panel cluster will come on.
SeeTow/Haul Mode Light on page 264for more
information.
Also see “Tow Haul Mode” underTowing a Trailer
on page 429for more information.
Grade Braking and Cruise Grade
Braking (Allison Transmission®)
Grade Braking and Cruise Grade Braking assists
when driving on a downhill grade. It maintains
the vehicle’s speed by automatically using a shift
schedule that uses the engine and the
transmission to slow the vehicle. This reduces
wear on the brakes system and increases control
of the vehicle. The system constantly monitors
the vehicle’s speed, acceleration, engine torque,
and brake pedal usage. It detects when the
truck is on a downhill grade and the driver’s desire
to slow down by pressing the brake.
148