2010 GMC SIERRA DENALI transmission

Automatic Transmission Operation
The vehicle has a Hydra-Matic®6L80 automatic
transmission, and has an electronic shift position
indicator within the instrument panel cluster. The
electronic shift position indicator displays when the shift
lever is moved out of P (Park).
There are several different positions for the shift lever.
Light Duty 6‐Speed Automatic Transmission Shown (Heavy Duty 6‐Speed Similar)
See “Range Selection Mode” later in this section.
P (Park) : This position locks your rear wheels. It is the
best position to use when you start the engine because
the vehicle cannot move easily.
When parked on a hill, especially when the vehicle has
a heavy load, you may notice an increase in the effort to
shift out of P (Park). See Torque Lock (Automatic
Transmission) under Shifting Into Park
on page 3‑35for more information.
{WARNING:
It is dangerous to get out of the vehicle if the shift
lever is not fully in P (Park) with the parking brake
firmly set. The vehicle can roll.
Do not leave the 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 the
vehicle will not move, even when you are on fairly
level ground, always set the parking brake and
move the shift lever to P (Park). See Shifting Into
Park
on page 3‑35. If you are pulling a trailer,
see Towing a Trailer on page 5‑42.
R (Reverse) : Use this gear to back up.
Notice: Shifting to R (Reverse) while the vehicle is
moving forward could damage the transmission.
The repairs would not be covered by the vehicle
warranty. Shift to R (Reverse) only after the vehicle
is stopped.
To rock the vehicle back and forth to get out of snow,
ice, or sand without damaging the transmission, see If
Your Vehicle is Stuck in Sand, Mud, Ice, or Snow
on
page 5‑29.
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N (Neutral) :In this position, the engine does not
connect with the wheels. To restart the engine when the
vehicle is already moving, use N (Neutral) only. Also,
use N (Neutral) when the vehicle is being towed.
{WARNING:
Shifting into a drive gear while the engine is
running at high speed is dangerous. Unless your
foot is firmly on the brake pedal, the vehicle could
move very rapidly. You could lose control and hit
people or objects. Do not shift into a drive gear
while the engine is running at high speed.
Notice: Shifting out of P (Park) or N (Neutral) with
the engine running at high speed may damage the
transmission. The repairs would not be covered by
the vehicle warranty. Be sure the engine is not
running at high speed when shifting the vehicle. D (Drive) :
This position is for normal driving. It provides
the best fuel economy for the vehicle. If you need more
power for passing, and you are:
.Going less than about 35 mph (55 km/h), push the
accelerator pedal about halfway down.
.Going about 35 mph (55 km/h) or more, push the
accelerator all the way down.
D (Drive) 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 a lower gear
selection if the transmission shifts too often.
Downshifting the transmission in slippery road
conditions could result in skidding, see “Skidding”under
Loss of Control on page 5‑11.
When temperatures are very cold, the Hydra-Matic
®
Automatic Transmission's gear shifting may be delayed
providing more stable shifts until the engine warms up.
Shifts may be more noticeable with a cold transmission.
This difference in shifting is normal.
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M (Manual Mode) :This position lets drivers select the
range of gears appropriate for current driving
conditions. See Range Selection Mode later in this
section.
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 the vehicle warranty. If you are stuck, do
not spin the tires. When stopping on a hill, use the
brakes to hold the vehicle in place.
The vehicle has 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 a 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 vehicle's transmission uses adaptive shift controls.
Adaptive shift controls continually compares key shift
parameters to pre‐programmed ideal shift conditions
stored in the transmissions computer. The 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 the best settings for a
particular shift.
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Range Selection Mode
On vehicles with a Range Selection Mode, this feature
may be used to control the vehicle's transmission.
To use this feature, do the following:1. Move the shift lever to the M (Manual Mode).
2. Press the plus/minus button, to upshift or downshift selecting the desired range of gears for current
driving conditions. When in M (Manual Mode) a number displays next to
the M, indicating the current gear that has been
selected. The number displayed in the gear indicator is
the highest gear that can be used. However, the vehicle
can automatically shift to lower gears as it adjusts to
driving conditions. This means that all gears below that
number are available. When 5 (Fifth) is selected,
1 (First) through 5 (Fifth) gears are automatically shifted
by the vehicle, but 6 (Sixth) cannot be used until the
plus/minus button located on the steering column lever
is used to change to the gear.
Range Selection Mode controls the vehicle and engine
speed while driving down a hill or towing a trailer, by
allowing you to select a desired range of gears.
Grade Braking is not available when the Range
Selection Mode is active. See
Tow/Haul Mode
on
page 3‑32for more information.
While using the Range Selection Mode, Cruise Control
and the Tow/Haul mode can be used.
3-31

Tow/Haul Mode
The vehicle has a tow/haul mode. The tow/haul mode
adjusts the transmission shift pattern to reduce shift
cycling, providing increased performance, vehicle
control, and transmission cooling while towing or
hauling heavy loads.Press the button located on the end of the shift lever to
turn the tow/haul on or off. While the tow/haul is on, a
light on the instrument panel cluster comes on.
See
Tow/Haul Mode Light
on page 4‑43for more
information.
Also see “Tow Haul Mode” underTowing a Trailer
on
page 5‑42for more information.
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Grade Braking
The Grade Braking shift modes can be activated by
pressing the button on the end of the shift control lever.
While in Range Selection Mode , Grade Braking is
deactivated allowing the driver to select a desired range
of gears.
Grade Braking is only active while the Tow/Haul Mode
is selected and you are not in the Range Selection
Mode. See“Tow/Haul Mode listed previously and
Automatic Transmission Operation
on page 3‑28for
more information on the Range Selection Mode. Grade
Braking assists in maintaining desired vehicle speeds
when driving on downhill grades by automatically
implementing a shift schedule that utilizes the engine
and transmission to slow the vehicle. This reduces wear
on the braking system and increases control of the
vehicle. Grade Braking monitors vehicle speed,
acceleration, engine torque and brake pedal usage.
Using this information, it detects when the truck is on a
downhill grade and the driver desires to slow the vehicle
by pressing the brake.
Also see Towing a Trailer
on page 5‑42for more
information.
Cruise Grade Braking
Cruise Grade Braking assists when driving on a
downhill grade. It maintains vehicle speed by
automatically implementing a shift schedule that uses
the engine and the transmission to slow the vehicle.
Cruise Grade Braking operates while Cruise Control is
engaged in Tow/Haul mode to assist in maintaining
vehicle speed under loaded vehicle conditions.
It utilizes vehicle acceleration and deviation from
desired speed to determine the correct gear for the
operating condition. If vehicle speed is above the
desired speed the transmission will downshift to slow
the vehicle. If vehicle speed is near or below desired
speed the trans will upshift, allowing vehicle speed to
increase.
While in the Range Select Mode (RSM) mode, cruise
grade braking is not available.
See Automatic Transmission Operation on page 3‑28.
3-33

Torque Lock
If you are parking on a hill and you do not shift the
transmission into P (Park) properly, the weight of the
vehicle can put too much force on the parking pawl in
the transmission. It might be difficult to pull the shift
lever out of P (Park). This is called torque lock. To
prevent torque lock, set the parking brake and then shift
into P (Park) properly before you leave the driver seat.
To find out how, seeShifting Into Park on page 3‑35.
When you are ready to drive, move the shift lever out of
P (Park) before releasing the parking brake.
If torque lock does occur, you might need to have
another vehicle push yours a little uphill to take some of
the pressure from the parking pawl in the transmission.
Then you should be able to pull the shift lever out of
P (Park).
Shifting Out of Park
This vehicle is equipped with an electronic shift lock
release system. The shift lock release is designed to:
.Prevent ignition key removal unless the shift lever
is in P (Park) with the shift lever button fully
released, and
.Prevent movement of the shift lever out of P (Park),
unless the ignition is in ON/RUN or ACC/
ACCESSORY and the regular brake pedal is
applied. The shift lock release is always functional except in the
case of an uncharged or low voltage (less than 9 volt)
battery.
If the vehicle has an uncharged battery or a battery
with low voltage, try charging or jump starting the
battery. See
Jump Starting
on page 6‑44for more
information.
To shift out of P (Park) use the following:
1. Apply the brake pedal.
2. Move the shift lever to the desired position.
If you still are unable to shift out of P (Park): 1. Ease the pressure on the shift lever.
2. While holding down the brake pedal, press the shift lever all the way into P (Park).
3. Move the shift lever to the desired position.
If you are still having a problem shifting, then have the
vehicle serviced soon.
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Running the Vehicle While Parked
It is better not to park with the engine running. But if you
ever have to, here are some things to know.
{WARNING:
Idling a vehicle in an enclosed area with poor
ventilation is dangerous. Engine exhaust may
enter the vehicle. Engine exhaust contains
Carbon Monoxide (CO) which cannot be seen or
smelled. It can cause unconsciousness and even
death. Never run the engine in an enclosed area
that has no fresh air ventilation. For more
information, seeEngine Exhaust on page 3‑37.
{WARNING:
It can be dangerous to get out of the vehicle if the
automatic transmission shift lever is not fully in
P (Park) with the parking brake firmly set. The
vehicle can roll. Do not leave the 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 the vehicle will not move, even when you are
on fairly level ground, always set the parking
brake and move the shift lever to P (Park).
Follow the proper steps to be sure the vehicle will not
move. See Shifting Into Park on page 3‑35.
If parking on a hill and pulling a trailer, see Towing a
Trailer on page 5‑42.
3-38