Transmission GMC SIERRA 2020 Owner's Guide

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
Driving and Operating 221
If the vehicle is left with the engine
running, follow the proper steps to
be sure the vehicle will not move.
SeeShifting Into Park 0217 and
Engine Exhaust 0220.
If parking on a hill and pulling a
trailer, see Driving Characteristics
and Towing Tips 0287.Automatic
Transmission
If equipped, there is an electronic
shift lever position indicator within
the instrument cluster. This display
comes on when the ignition is in
ACC/ACCESSORY, on or
service mode.
There are several different positions
for the shift lever.
See Driver Mode Control 0238 and
“Range Selection Mode” under
Manual Mode 0224.
P : This position locks the rear
wheels. Use P (Park) when starting
the engine because the vehicle
cannot move easily.
When parked on a hill, especially
when the vehicle has a heavy load,
you might notice an increase in the effort to shift out of P (Park). See
“Torque Lock”
underShifting Into
Park 0217.
{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. 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 0217 and
Driving Characteristics and
Towing Tips 0287.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
222 Driving and Operating
{Warning
If equipped with four-wheel drive,
the vehicle will be free to roll if the
transfer case is in N (Neutral),
even when the shift lever is in
P (Park). You or someone else
could be seriously injured. Be
sure the transfer case is in a drive
gear—2
m, 4m, or 4n—or set the
parking brake before placing the
transfer case in N (Neutral). See
Four-Wheel Drive 0227.
R : Use this gear to back up.
Caution
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
the Vehicle Is Stuck 0199.
N : 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.
Caution
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.
Caution
A transmission or engine oil hot
message may display if the
automatic transmission fluid or
engine oil is too hot. Driving
under this condition can damage
the vehicle. Stop and idle the
engine to cool the engine oil or
automatic transmission fluid.
These messages will clear when
the engine oil or transmission
fluid has cooled sufficiently.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
Driving and Operating 223
D :This position is for normal
driving. It provides the best fuel
economy. If more power is needed
for passing, press the accelerator
pedal down.
. When going less than about 55
km/h (35 mph), push the
accelerator pedal about
halfway down.
. When going about 55 km/h (35
mph) or more, push the
accelerator all the way down.
By doing this, the vehicle shifts
down to the next gear and has
more power.
Use D (Drive) and Tow/Haul Mode
when towing a trailer, carrying a
heavy load, driving on steep hills,
or driving off-road. Shift the
transmission to a lower gear if the
transmission shifts too often.
Downshifting the transmission in
slippery road conditions could result
in skidding. See “Skidding”under
Loss of Control 0190. 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 is able to
maintain vehicle speed by analyzing
things such as vehicle speed,
throttle position, and vehicle load.
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 could appear to
be a delayed shift, however the
transmission is operating normally.
If the engine or transmission detects
an impending hot fluid condition, the
transmission may upshift to limit
temperatures. Downshifts may also
be prevented. Normal operation
may continue unless the display
indicates there is a hot condition
and engine should be idled. The transmission uses adaptive
shift controls. The adaptive shift
control process continually
compares key shift parameters to
pre-programmed ideal shifts stored
in the transmission’s computer. The
transmission constantly makes
adjustments to improve vehicle
performance according to how the
vehicle is being used, such as with
a heavy load or when the
temperature changes. During this
adaptive shift control process,
shifting might feel different as the
transmission determines the best
settings.
When temperatures are very cold,
the transmission's gear shifting
could be delayed providing more
stable shifts until the engine warms
up. Shifts could be more noticeable
with a cold transmission. This
difference in shifting is normal.
If equipped with the 2.7L L4 engine,
engine speeds may be increased
while driving at highway speeds
while the engine is still warming up.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
224 Driving and Operating
L :This position allows selection of
a range of gears appropriate for
current driving conditions.
If equipped, see “Range Selection
Mode” underManual Mode 0224.
Caution
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 the vehicle
is stuck, do not spin the tires.
When stopping on a hill, use the
brakes to hold the vehicle in
place.
Manual Mode
Range Selection Mode
Range Selection Mode helps control
the vehicle's transmission and
vehicle speed while driving downhill
or towing a trailer by letting you
select a desired range of gears.
To use this feature:
1. Move the shift lever to L (Manual Mode).
2. Press the plus/minus buttons on the shift lever to select the
desired range of gears for
current driving conditions.
When the shift lever is moved from
D (Drive) to L (Manual Mode), a
number displays next to the L,
indicating the current transmission
range. This number is the highest gear that
the transmission will command while
operating in L (Manual Mode). All
gears below that number are
available. As driving conditions
change, the transmission can
automatically shift to lower gears.
For example, when L5 is selected,
1 (First) through 5 (Fifth) gears are
automatically shifted by the
transmission, but 6 (Sixth) cannot be
used until the plus/minus button on
the shift lever is used to change to
the range.
When the shift lever is moved from
D (Drive) to L (Manual Mode), a
downshift may occur. The gear that
the transmission is operating in
when the shift lever is moved from
D (Drive) to L (Manual Mode)
determines if a downshift occurs.
See the following charts.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
Driving and Operating 225
6-Speed Automatic TransmissionGear before shifting from
D (Drive) to L (Manual Mode) 6th 5th 4th 3rd 2nd 1st
Range after shifting from
D (Drive) to L (Manual Mode) L4 L4 L3 L2 L2 L1
8-Speed Automatic Transmission Gear before
shifting from
D (Drive) to
L (Manual Mode) 8th 7th 6th 5th 4th 3rd 2nd 1st
Range after
shifting from
D (Drive) to
L (Manual Mode) –
Tow/Haul not
engaged L6 L6 L5 L4 L3 L3 L2 L1
Range after
shifting from
D (Drive) to
L (Manual Mode) –
Tow/Haul engaged L6 L5 L4 L3 L3 L3 L2 L1

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
226 Driving and Operating
10-Speed Automatic TransmissionGear before shifting from D (Drive) to
L (Manual Mode) 10th 9th 8th 7th 6th 5th 4th 3rd 2nd 1st
Range after shifting from D (Drive) to
L (Manual Mode) - Tow/Haul not engaged L7 L7 L7 L6 L5 L4 L3 L3 L2 L1
Range after shifting from D (Drive) to
L (Manual Mode) - Tow/Haul engaged L7 L7 L6 L5 L4 L3 L3 L3 L2 L1
Grade Braking is not available when
Range Selection Mode is active.
See Tow/Haul Mode 0226.
While using Range Selection Mode,
cruise control and the Tow/Haul
Mode can be used.
If the vehicle has an exhaust brake,
it can also be used, but will not
automatically downshift the
transmission. See “Exhaust Brake”
in the Duramax diesel supplement.
Caution
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 the vehicle
is stuck, do not spin the tires.
When stopping on a hill, use the
brakes to hold the vehicle in
place.
Low Traction Mode
If equipped, Low Traction Mode
assists in vehicle acceleration when
road conditions are slippery, such as with ice or snow. While the
vehicle is at a stop, select L2 using
Range Selection Mode. This will
limit torque to the wheels and help
prevent the tires from spinning.
Tow/Haul Mode
The Tow/Haul Mode adjusts the
transmission shift pattern to reduce
shift cycling. This provides
increased performance, vehicle
control, and enhanced transmission
and engine cooling when driving
down steep hills or mountain
grades, when towing, or when
hauling heavy loads. See
Driver
Mode Control 0238 to activate Tow/
Haul Mode.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
Driving and Operating 227
For vehicles without Driver Mode
Control, press the Tow/Haul button
on the center stack.
If equipped, the Stop/Start system
will become unavailable when Tow/
Haul Mode is active.
Tow/Haul Mode Grade Braking
Tow/Haul Mode Grade Braking is
only enabled while the Tow/Haul
Mode is selected and the vehicle is
not in the Range Selection Mode.
SeeManual Mode 0224. Tow/Haul
Mode Grade Braking assists in
maintaining desired vehicle speeds
when driving on downhill grades by
using the engine and transmission
to slow the vehicle.
See Towing Equipment 0296.
Drive Systems
Four-Wheel Drive
If equipped, four-wheel drive
engages the front axle for extra
traction.
Read the appropriate section for
transfer case operation before
using.
Caution
Do not drive on clean, dry
pavement in 4
mand 4n(if
equipped) for an extended period
of time. These conditions may
cause premature wear on the
vehicle’s powertrain.
Driving on clean, dry pavement in 4
mor 4nmay:
. Cause a vibration to be felt in
the steering system.
. Cause tires to wear faster.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
Driving and Operating 229
automatically based on driving
conditions. This setting provides
slightly lower fuel economy than 2
m.
4
m(Four-Wheel Drive High) : Use
this setting when extra traction is
needed, such as when driving on
snowy or icy roads, when
off-roading, or when plowing snow.
4
n(Four-Wheel Drive Low) : This
setting engages the front axle and
delivers extra torque. Choose 4
n
when driving off-road in deep sand,
deep mud, or deep snow, and while
climbing or descending steep hills.
While driving in 4
n, keep vehicle
speed below 72 km/h (45 mph).
Shifting into 4
nwill turn Traction
Control and StabiliTrak/ESC off.
See Traction Control/Electronic
Stability Control 0235.
Shifts between 2
m, 4m, and AUTO
Any of these shifts can be made at
normal driving speed. The actual 4x4 shift request is only
made after the button is released.
The 4x4 graphic will remain flashing
until the shift request has
completed. A DIC message displays
to indicate that the 4x4 transfer case
has been requested to shift to the
new desired state.
Once the 4x4 shift has completed,
the DIC message disappears, the
4x4 graphic stops flashing, and the
current setting is indicated.
When a shift to 2
mis completed
successfully while in P (Park), the
parking brake will engage. To
resume driving, shift the
transmission to the desired gear
and manually release the parking
brake or press the accelerator pedal
to begin driving. See Electric
Parking Brake 0233.
If equipped, use 4
n, AUTO, or 4mto
provide additional traction when
parking on a steep grade with poor
traction such as ice, snow, mud,
or gravel. Shifting Into 4
n
1. The ignition must be on 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. Press 4
n. The actual 4x4 shift
request is only made after the
button is released. The 4x4
graphic will remain flashing
until the shift request has
completed. A DIC message
displays to indicate that the 4x4
transfer case has been
requested to shift to the new
desired state.
Once the 4x4 shift has
completed, the DIC message
disappears, the 4x4 graphic
stops flashing and the current
setting is indicated.
If vehicle speed is higher when shift
request occurs, a DIC message
displays. Reduce vehicle speed.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
230 Driving and Operating
If the transmission is not in
N (Neutral) when shift request
occurs, a DIC message displays.
The vehicle will allow 20 seconds
for the shift to occur. After this time,
a graphic in the instrument cluster
will indicate that the transfer case is
in 4
n.
Caution
Shifting the transmission into gear
before the requested mode
indicator light has stopped
flashing could damage the
transfer case.
If the transmission is not shifted into
N (Neutral) or the vehicle has not
slowed to 5 km/h (3 mph) within
20 seconds, the transfer case will
remain in its original state. This will
be indicated in the instrument
cluster.
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
n
1. The vehicle must be stopped or
moving less than 5 km/h
(3 mph) with the transmission
in N (Neutral) and the ignition
on. It is best for the vehicle to
be moving
1.6 to 3.2 km/h (1 to 2 mph).
2. Press 4
m, AUTO, or 2m. The
actual 4x4 shift request is only
made after the button is
released. The 4x4 graphic will
remain flashing until the shift
request has completed. A DIC
message displays to indicate
the state of the request.
Once the 4x4 shift has
completed, the DIC message
disappears, the 4x4 graphic
stops flashing, and the current
setting is indicated.
If vehicle speed is higher when
shift request occurs, a DIC
message displays. Reduce
vehicle speed. If the transmission is not in
N (Neutral) when shift request
occurs, DIC messages will display.
The vehicle will allow 20 seconds
for this shift to occur. After this time,
a graphic in the instrument cluster
will indicate that the transfer case is
in 4
n.
Caution
Shifting the transmission into gear
before the requested mode
indicator light has stopped
flashing could damage the
transfer case.
If the transmission is not shifted into
N (Neutral) or the vehicle has not
slowed to 5 km/h (3 mph) within
20 seconds, the transfer case will
remain in its original state. This will
be indicated in the instrument
cluster.
With the vehicle moving less than
5 km/h (3 mph), and the
transmission in N (Neutral), attempt
the shift again.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
Driving and Operating 231
Shifting Into N (Neutral)
To shift into N (Neutral):1. Start the vehicle.
2. Shift the transmission to N (Neutral).
3. Shift the transfer case to 2
m.
4. Apply the parking brake and/or brake pedal.
5. Press 2
mfive times in
10 seconds until the N (Neutral)
graphic starts flashing in the
instrument cluster. When the
shift is complete, the graphic
stops flashing. If the parking
brake and/or brake pedal is not
applied within 20 seconds, the
transfer case will remain in the
original state.
6. If the transmission is not shifted into N (Neutral) or the
vehicle has not slowed to
5 km/h (3 mph) within
20 seconds, the transfer case
will remain in its original state.
This will be indicated in the
instrument cluster. Shifting Out of N (Neutral)
To shift out of N (Neutral):
1. Turn the ignition on with the engine off. See Ignition
Positions (Keyless Access)
0 208 or
Ignition Positions (Key Access)
0 210.
2. Set the parking brake. See Electric Parking Brake 0233.
3. Shift the transmission to N (Neutral).
4. Shift the transfer case to 2
m.
Transfer case shifts out of
N (Neutral) can only be made
into 2
m. When the shift to 2mis
complete, the graphic in the
instrument cluster will stop
flashing. If the transfer case
cannot complete a shift, the
graphic will return to the
previously selected setting. Single Speed Transfer Case
If equipped, the transfer case
controls are used to shift into and
out of four-wheel drive.
To shift the transfer case, press the
desired button. The graphic in the
instrument cluster will flash while a
shift is in progress. The graphic
displayed will change to indicate the
setting requested.
When the shift is complete the
graphic will stop flashing. The DIC
message turns off once the shift is
complete. If the transfer case