engine GMC SIERRA 2023 Repair Manual

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
Localizing-U.S./Canada-16504257) - 2023 - CRC - 5/9/22
Driving and Operating 223
Caution
Use the correct key, make sure it is all
the way in—or pushed all the way in
toward the steering column when turning
off the vehicle —and turn it only with
your hand.
1 (ACC/ACCESSORY) : This position allows
features such as the infotainment system to
operate while the vehicle is off. It also
unlocks the steering column, if equipped
with a locking steering column. Use this
position if the vehicle must be pushed or
towed. See Retained Accessory Power (RAP)
0 227.
From ON/RUN, push the key all the way in
toward the steering column, then turn the
key to ACC/ACCESSORY.
If the key is left in ACC/ACCESSORY with the
engine off, the battery could drain and the
vehicle may not start.
A warning chime will sound when the driver
door is opened and the key is in the
ignition.
2 (ON/RUN) : This position can be used to
operate the electrical accessories and to
display some instrument cluster warning
and indicator lights. This position can also be used for service and diagnostics, and to
verify the proper operation of the
malfunction indicator lamp as may be
required for emission inspection purposes.
The switch stays in this position when the
engine is running. The transmission is also
unlocked in this position.
If the key is left in ON/RUN with the engine
off, the battery could drain and the vehicle
may not start.
3 (START) :
This is the position that starts
the engine. When the engine starts, release
the key. The ignition returns to ON/RUN for
driving.
Ignition Positions (Keyless Access)
Vehicles equipped with Keyless Access have
pushbutton starting.
The remote key must be in the vehicle for
the system to operate. If the pushbutton
start is not working, the vehicle may be
near a strong radio antenna signal causing
interference to the Keyless Access system.
See Remote Keyless Entry (RKE) System
Operation (Key Access) 012 or
Remote Keyless Entry (RKE) System
Operation (Keyless Access) 014.
To shift out of P (Park), the ignition must be
on or in Service Mode, and the brake pedal
must be applied.
{Warning
Turning off the vehicle while moving may
cause loss of power assist in the brake
and steering systems and disable the
airbags. While driving, only shut the
vehicle off in an emergency.
Stopping the Engine/LOCK/OFF (No Indicator
Lights) : When the vehicle is stopped, press
ENGINE START/STOP once to turn the
engine off.

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
Localizing-U.S./Canada-16504257) - 2023 - CRC - 5/9/22
224 Driving and Operating
If the vehicle is in P (Park), the ignition will
turn off, and Retained Accessory Power (RAP)
will remain active. SeeRetained Accessory
Power (RAP) 0227.
If the vehicle is not in P (Park), the ignition
will return to accessory mode and display
the message SHIFT TO PARK in the Driver
Information Center (DIC). When the vehicle is
shifted into P (Park), the ignition system will
turn off.
The vehicle may have an electric steering
column lock. The lock is activated when the
ignition is turned off and driver door is
opened. A sound may be heard as the lock
actuates or releases. The steering column
lock may not release with the wheels turned
off center. If this happens, the vehicle may
not start. Move the steering wheel from left
to right while attempting to start the
vehicle. If this does not work, the vehicle
needs service.
Unless an emergency exists, do not turn the
engine off when the vehicle is moving. This
will cause a loss of power assist in the brake
and steering systems and disable the
airbags.
If the vehicle must be shut off in an
emergency: 1. If the vehicle cannot be pulled over, and
must be shut off while driving, press and
hold ENGINE START/STOP button for
longer than two seconds, or press twice
in five seconds.
2. Brake using a firm and steady pressure. Do not pump the brakes repeatedly. This
may deplete power assist, requiring
increased brake pedal force.
3. Shift the vehicle to N (Neutral). This can be done while the vehicle is moving.
After shifting to N (Neutral), firmly apply
the brakes and steer the vehicle to a
safe location.
4. Come to a complete stop, shift to P (Park), and make sure engine is off.
The shift lever must be in P (Park) to
turn the ignition off.
5. Set the parking brake. See Electric
Parking Brake 0239.
{Warning
Turning off the vehicle while moving may
cause loss of power assist in the brake
and steering systems and disable the
airbags. While driving, only shut the
vehicle off in an emergency. Accessory Mode (Amber Indicator Light) :
This mode allows some electrical accessories
to be used when the engine is off.
With the ignition off, pressing the button
once without the brake pedal applied will
place the ignition system in accessory mode.
The ignition will switch from accessory
mode to OFF after five minutes to prevent
battery rundown.
ON/RUN/START (Green Indicator Light) :
This
mode is for driving and starting. With the
ignition off, and the brake pedal applied,
pressing ENGINE START/STOP button once
will turn the ignition on. Once engine
cranking begins, release the button. Engine
cranking will continue until the engine
starts. See Starting the Engine 0225.
Service Mode
This power mode is available for service and
diagnostics, and to verify the proper
operation of the malfunction indicator lamp
as may be required for emission inspection
purposes. With the vehicle off, and the
brake pedal not applied, pressing and
holding the ENGINE START/STOP button for
more than five seconds will place the vehicle
in Service Mode. The instruments and audio
systems will operate as they do when the

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
Localizing-U.S./Canada-16504257) - 2023 - CRC - 5/9/22
Driving and Operating 225
ignition is on, but the vehicle will not
be able to be driven. The engine will not
start in Service Mode. Press the ENGINE
START/STOP button again to turn the
ignition off.
Starting the Engine
If the vehicle has a diesel engine, see the
Duramax diesel supplement.
Caution
If you add electrical parts or accessories,
you could change the way the engine
operates. Any resulting damage would
not be covered by the vehicle warranty.
SeeAdd-On Electrical Equipment 0297.
Move the shift lever to P (Park) or
N (Neutral). To restart the engine when the
vehicle is already moving, use
N (Neutral) only.
Caution
Do not try to shift to P (Park) if the
vehicle is moving. If you do, you could
damage the transmission. Shift to P (Park)
only when the vehicle is stopped.
Starting Procedure
1. For Key Access vehicles, turn the ignition key to Start. When the engine starts, let
go of the key. For Keyless Access
vehicles, the remote key must be in the
vehicle. Press ENGINE START/STOP with
the brake pedal applied. When the
engine begins cranking, let go of the
button.
The driver may observe a minor, and
temporary, brake pedal kickback when
starting the vehicle. This is normal.
The idle speed will go down as the
engine gets warm. Do not race the
engine immediately after starting it.
Operate the engine and transmission
gently to allow the oil to warm up and
lubricate all moving parts.
When the low fuel warning light is on
and the FUEL LEVEL LOW message is
displayed in the Driver Information
Center (DIC), hold the ignition switch in
the START position to continue engine
cranking.Caution
Cranking the engine for long periods of
time, by returning the ignition to the
START position immediately after
cranking has ended, can overheat and
damage the cranking motor, and drain
the battery. Wait at least 15 seconds
between each try, to let the cranking
motor cool down.
2. If the engine does not start after five to 10 seconds, especially in very cold
weather (below −18 °C or 0 °F), it could
be flooded with too much gasoline. Try
pushing the accelerator pedal all the way
to the floor and holding it there while
holding the key in START or ENGINE
START/STOP for up to a maximum of
15 seconds. Wait at least 15 seconds
between each try, to allow the cranking
motor to cool down. When the engine
starts, let go of the key or button and
accelerator. If the vehicle starts briefly
but then stops again, do the same thing.
This clears the extra gasoline from the
engine. Do not race the engine
immediately after starting it. Operate

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
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226 Driving and Operating
the engine and transmission gently until
the oil warms up and lubricates all
moving parts.
Engine Heater
If equipped, the engine heater can provide
easier starting and better fuel economy
during engine warm-up in cold weather
conditions at or below−18 °C (0 °F). Vehicles
with an engine heater should be plugged in
at least four hours before starting. An
internal thermostat in the plug-end of the
cord may exist, which will prevent engine
heater operation at temperatures above
−18 °C (0 °F).
{Warning
Do not plug in the engine block heater
while the vehicle is parked in a garage or
under a carport. Property damage or
personal injury may result. Always park
the vehicle in a clear open area away
from buildings or structures.
To Use the Engine Heater
1. Turn off the engine.
2. Check the heater cord for damage. If it is damaged, do not use it. See your dealer
for a replacement. Inspect the cord for
damage yearly.
3. Plug the heater cord into the connector in the front fascia.
4. Plug the cord into a grounded 110-volt AC outlet that is protected by a ground
fault detection function.
{Warning
Improper use of the heater cord or an
extension cord can damage the cord and
may result in overheating and fire.
.Plug the cord into a three-prong
electrical utility receptacle that is
protected by a ground fault detection
function. An ungrounded outlet could
cause an electric shock.
.Use a weatherproof, heavy-duty,
15 amp-rated extension cord if needed.
Failure to use the recommended
extension cord in good operating
condition, or using a damaged heater
or extension cord, could make it
overheat and cause a fire, property
damage, electric shock, and injury.
.Do not operate the vehicle with the
heater cord permanently attached to
the vehicle. Possible heater cord and
thermostat damage could occur.
.While in use, do not let the heater
cord touch vehicle parts or sharp
edges. Never close the hood on the
heater cord.
(Continued)

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
Localizing-U.S./Canada-16504257) - 2023 - CRC - 5/9/22
Driving and Operating 227
Warning (Continued)
.Before starting the vehicle, unplug the
cord, reattach the cover to the plug,
and securely fasten the cord. Keep the
cord away from any moving parts.
5. Before starting the engine, be sure to unplug and store the cord.
The length of time the heater should remain
plugged in depends on several factors. Ask a
dealer in the area where you will be parking
the vehicle for the best advice on this.
Retained Accessory Power (RAP)
When the vehicle is turned from on to off,
the following features (if equipped) will
continue to function for up to 10 minutes,
or until the driver door is opened. These
features will also work when the vehicle is
on or in accessory mode:
.Infotainment System
.Power Windows (during RAP this
functionality will be lost when any door
is opened)
.Sunroof (during RAP this functionality will
be lost when any door is opened)
.Auxiliary Power Outlet
.Audio System
.OnStar System
Shifting Into Park
{Warning
Parking on grades with poor traction such
as ice, snow, mud, or gravel may cause
the vehicle to unintentionally move and
could result in injury, death, and/or
vehicle damage. If equipped with
four-wheel drive, use AUTO or 4 (HI) to
provide additional traction. Be sure to
apply the parking brake. See Electric
Parking Brake 0239 and
Four-Wheel Drive 0234.
{Warning
It can be 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. 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,
(Continued)
Warning (Continued)
use the steps that follow. With
four-wheel drive, if the transfer case is in
N (Neutral), the vehicle will be free to
roll, even if the shift lever is in P (Park).
Be sure the transfer case is in a drive
gear. If towing a trailer, seeDriving
Characteristics and Towing Tips 0268.
1. Hold the brake pedal down, then set the parking brake. See Electric Parking Brake
0 239.
2. Move the shift lever into the P (Park) position by pulling the shift lever toward
you and moving it up as far as it will go.
3. Be sure the transfer case (if equipped) is in a drive gear –not in N (Neutral).
4. Turn the ignition off. For Key Access, push the ignition key in, towards the
steering column and then turn the
ignition off.
5. For Key Access, remove the key and take it with you. If you can leave the vehicle
with the ignition key in your hand, the
vehicle is in P (Park).
For Keyless Access, take the remote key
with you.

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
Localizing-U.S./Canada-16504257) - 2023 - CRC - 5/9/22
228 Driving and Operating
Leaving the Vehicle with the Engine
Running
{Warning
It can be dangerous to leave the vehicle
with the engine running. The vehicle
could move suddenly if the shift lever is
not fully in P (Park) with the parking
brake firmly set.
If you have four-wheel drive and the
transfer case is in N (Neutral), the vehicle
will be free to roll, even if the shift lever
is in P (Park). So be sure the transfer case
is in a drive gear–not in N (Neutral).
And, if you leave the vehicle with the
engine running, it could overheat and
even catch fire. You or others could be
injured. Do not leave the vehicle with the
engine running unless you have to.
If you have to leave the vehicle with the
engine running, be sure the vehicle is in
P (Park) and the parking brake is firmly set
before you leave it. After moving the shift
lever into P (Park), hold the regular brake
pedal down. Then, see if you can move the
shift lever away from P (Park) without first pulling it toward you. If you can, it means
that the shift lever was not fully locked into
P (Park).
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 may put too much
force on the parking pawl in the
transmission. You may find it 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.
When you are ready to drive, move the
shift lever out of P (Park) 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. You will
then 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 system is
designed to prevent movement of the shift
lever out of P (Park), unless the brake pedal
is applied and the ignition is on or in
Service Mode.
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 or low
voltage battery, try charging or jump
starting the battery. See Jump Starting -
North America 0367.
To shift out of P (Park): 1. Apply the brake pedal.
2. Release the parking brake if it is applied. See Electric Parking Brake 0239.
3. Pull the shift lever toward you, then move it to the desired position, and
release.
If the vehicle still cannot be shifted out of
P (Park): 1. Ease the pressure on, or release the shift lever.
2. While holding the brake pedal, push the shift lever all the way into P (Park).
3. Pull the shift lever toward you, then move it to the desired position, and
release.

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Driving and Operating 229
If there is still a problem shifting, have the
vehicle serviced soon.
Parking over Things That Burn
{Warning
Things that can burn could touch hot
exhaust parts under the vehicle and
ignite. Do not park over papers, leaves,
dry grass, or other things that can burn.
Extended Parking
It is best not to park with the vehicle
running. If the vehicle is left running, be
sure it will not move and there is adequate
ventilation.
SeeShifting Into Park 0227 and
Engine Exhaust 0229.
If the vehicle is left parked and running with
the remote key outside the vehicle, it will
continue to run for up to 15 minutes.
If the vehicle is left parked and running with
the remote key inside the vehicle, it will
continue to run for up to 30 minutes.
The vehicle could turn off sooner if it is
parked on a hill, due to lack of
available fuel. The timer will reset if the vehicle is taken
out of P (Park) while it is running.
When the vehicle was produced, it came
with the auto-shutdown feature enabled.
If you are not the primary owner of your
vehicle, please note that this feature may
have been disabled by a previous owner.
The vehicle owners can have this feature
re-enabled at owner cost at any GM service
center.
Engine Exhaust
{
Warning
Engine exhaust contains carbon monoxide
(CO), which cannot be seen or smelled.
Exposure to CO can cause
unconsciousness and even death.
Exhaust may enter the vehicle if:
.The vehicle idles in areas with poor
ventilation (parking garages, tunnels,
deep snow that may block underbody
airflow or tail pipes).
.The exhaust smells or sounds strange
or different. (Continued)
Warning (Continued)
.The exhaust system leaks due to
corrosion or damage.
.The vehicle exhaust system has been
modified, damaged, or improperly
repaired.
.There are holes or openings in the
vehicle body from damage or
aftermarket modifications that are not
completely sealed.
If unusual fumes are detected or if it is
suspected that exhaust is coming into the
vehicle:
.Drive it only with the windows
completely down.
.Have the vehicle repaired immediately.
Never park the vehicle with the engine
running in an enclosed area such as a
garage or a building that has no fresh air
ventilation.

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
Localizing-U.S./Canada-16504257) - 2023 - CRC - 5/9/22
230 Driving and Operating
Running the Vehicle While Parked
It is better not to park with the engine
running.
If the vehicle is left with the engine running,
follow the proper steps to be sure the
vehicle will not move. SeeShifting Into Park
0 227 and
Engine Exhaust 0229.
If parking on a hill and pulling a trailer, see
Driving Characteristics and Towing Tips
0 268.
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 accessory mode, on,
or service mode. There are several different positions for the
shift lever.
See
Driver Mode Control 0243 and “Range
Selection Mode” underManual Mode 0232.
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 0227.
{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.
(Continued)
Warning (Continued)
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). SeeShifting
Into Park 0227 and
Driving Characteristics and Towing Tips
0 268.
{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 4
n— or set the parking brake before
placing the transfer case in N (Neutral).
See Four-Wheel Drive 0234.

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
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Driving and Operating 231
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
0 214.
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 hot message may display
if the automatic transmission fluid is too
hot. Driving under this condition can
damage the vehicle. Stop and idle the
engine to cool the automatic
transmission fluid. This message clears
when the transmission fluid has cooled
sufficiently.
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.

GMC Sierra/Sierra Denali 2500 HD/3500 HD Owner Manual (GMNA-
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232 Driving and Operating
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”underLoss of Control 0207.
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. 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.
L :
This position allows selection of a range
of gears appropriate for current driving
conditions. If equipped, see “Range Selection
Mode” underManual Mode 0232.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 transmission and vehicle speed while
driving downhill or towing a trailer.
It permits the manual selection of a desired
gear range.