2021 GMC SIERRA Exhaust system

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 221
Warning (Continued)
.Fully open the air outlets on or under
the instrument panel.
.Adjust the climate control system to
circulate the air inside the vehicle and
set the fan speed to the highest
setting. See“Climate Control Systems.”
For more information about CO, see
Engine Exhaust 0238.
To save fuel, run the engine for short
periods to warm the vehicle and then shut
the engine off and partially close the
window. Moving about to keep warm also
helps.
If it takes time for help to arrive, when
running the engine, push the accelerator
pedal slightly so the engine runs faster than
the idle speed. This keeps the battery
charged to restart the vehicle and to signal
for help with the headlamps. Do this as
little as possible, to save fuel.
If the Vehicle Is Stuck
Slowly and cautiously spin the wheels to
free the vehicle when stuck in sand, mud,
ice, or snow. See “Rocking the Vehicle to Get
It Out” later in this section. The Traction Control/Electronic Stability
Control can often help to free a stuck
vehicle. See
Traction Control/Electronic
Stability Control 0248. If TC/ESC cannot free
the vehicle, see “Rocking the Vehicle to Get
it Out” following.
{Warning
If the vehicle's tires spin at high speed,
they can explode, and you or others
could be injured. The vehicle can
overheat, causing an engine compartment
fire or other damage. Spin the wheels as
little as possible and avoid going above
56 km/h (35 mph).
For information about using tire chains on
the vehicle, see Tire Chains0379.
Rocking the Vehicle to Get It Out
Caution
Do not hold the steering wheel at full
rotation for more than 15 seconds and/or
at an elevated RPM. Damage may occur
to the power steering system and there
may be loss of power steering assist. Turn the steering wheel left and right to
clear the area around the front wheels. Then
make sure the wheels are pointed straight
ahead. For four-wheel-drive vehicles, shift
into Four-Wheel Drive High. Turn the TCS
off. Shift back and forth between R (Reverse)
and a forward gear, spinning the wheels as
little as possible. To prevent transmission
wear, wait until the wheels stop spinning
before shifting gears. Slowly spinning the
wheels in the forward and reverse directions
causes a rocking motion that could free the
vehicle. If that does not get the vehicle out
after a few tries, it might need to be towed
out. See
Towing the Vehicle 0394. Recovery
hooks can be used, if the vehicle has them.
Recovery Hooks
{Warning
Never pull on recovery hooks from the
side. The hooks could break and you and
others could be injured. When using
recovery hooks, always pull the vehicle
from the front.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 237
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 0391.
To shift out of P (Park): 1. Apply the brake pedal.
2. Release the parking brake if it is applied. See Electric Parking Brake 0247.
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.
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.
Active Fuel Management
If equipped, Active Fuel Management allows
a V8, V6, or L4 gasoline engine to operate
on either all of its cylinders, or a reduced
number of cylinders, depending on the
driving conditions. When less power is
required, such as cruising at a constant
vehicle speed, the system will enable
reduced cylinder operation, allowing the
vehicle to achieve better fuel economy.
When greater power is required, such as

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
238 Driving and Operating
accelerating from a stop, passing,
or merging onto a freeway, the system will
maintain full-cylinder operation.
Dynamic Fuel Management
If equipped, Dynamic Fuel Management
calculates the number of cylinders needed to
maximize fuel economy and meet the
driving demands. Dynamic Fuel Management
allows the engine to operate in multiple
possible configurations ranging from
zero-cylinder up to the full 8-cylinder
operation.
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 0236 and
Engine Exhaust 0238.
If the vehicle is left parked and running with
the RKE transmitter outside the vehicle, it
will continue to run for up to half an hour.
If the vehicle is left parked and running with
the RKE transmitter inside the vehicle, it will
continue to run for up to an hour. 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.
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.
.The exhaust system leaks due to
corrosion or damage.
.The vehicle exhaust system has been
modified, damaged, or improperly
repaired. (Continued)
Warning (Continued)
.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.
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. See Shifting Into Park
0 236 and
Engine Exhaust 0238.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
252 Driving and Operating
When you enter this mode, you will
immediately feel a down shift. In this mode
the vehicle also monitors driving behaviors
and automatically enables Performance Shift
Features when spirited driving is detected.
These features maintain lower transmission
gears to increase available engine braking
and improve acceleration response. The
vehicle will exit these features and return to
normal operation after a short period when
spirited driving is no longer detected. If the
vehicle has Magnetic Ride Control, the
suspension will change to provide better
cornering performance.
6Snow/Ice Mode :Snow/Ice Mode
improves vehicle acceleration on snow and
ice covered roads. When active, Snow/Ice
Mode will adjust acceleration to optimize
traction on slippery surfaces. This can
compromise the acceleration on dry asphalt.
This feature is not intended for use when
the vehicle is stuck in sand, mud, ice, snow,
or gravel. If the vehicle becomes stuck, see If
the Vehicle Is Stuck 0221.
7Off-Road Mode : Use this mode for
off-road recreational driving. Off-Road Mode
should be used to improve driving at
moderate speeds, on grass, gravel, dirt,
unpaved roads, or snow-covered roads. The accelerator pedal is tuned for off-road use.
This mode modifies pedal mapping,
All-Wheel Drive (AWD), ride height, Antilock
Brake System (ABS), StabiliTrak/Electronic
Stability Control (ESC), and Traction Control
System (TCS) performance.
For more information on off-road driving see
Off-Road Driving
0215.
_Tow/Haul Mode : Use this mode
when hauling heavy loads to provide
increased performance and vehicle control.
Tow/Haul Mode adjusts the transmission
shift pattern, AWD, and ESC performance.
If the vehicle is turned off with Tow/Haul
Mode active and then restarted within four
hours or less, Tow/Haul will remain active.
Otherwise, the vehicle will start in
Normal Mode.
If the vehicle has a diesel engine, exhaust
braking is automatically activated when
Tow/Haul Mode is selected. It maintains
vehicle speed by automatically
implementing a shift pattern that uses the
engine and the transmission to slow the
vehicle. The system will command
downshifts and use the turbocharger on the
engine to reduce vehicle speed when the
brake is applied. The normal tow/haul shift pattern will return once the vehicle is on a
low grade or when the accelerator pedal is
pressed.
While in the Electronic Range Select (ERS)
Mode (see
“manual mode”), grade breaking
is deactivated, allowing the driver to select a
range and limiting the highest gear
available.
For more information on trailer weight
specifications, see Towing Equipment 0296.
gTerrain Mode : Use for finer control
during low speed, off-road driving. When
using this mode it will mimic the
characteristics of four-wheel-drive low (4
n)
without the torque capabilities.
Use when:
.Traveling on very rough roads at very low
speeds, such as a two-track or heavily
rutted road.
.Traveling slowly in grassy fields.
.Pulling a boat out of the water on a
trailer.
.Using the vehicle for public off-road
recreational driving. See Off-Road Driving
0 215 and
Hill and Mountain Roads 0219.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
290 Driving and Operating
{Warning
To prevent serious injury or death from
carbon monoxide (CO), when towing a
trailer:
.Do not drive with the liftgate, trunk/
hatch, or rear-most window open.
.Fully open the air outlets on or under
the instrument panel.
.Adjust the climate control system to a
setting that brings in only outside air.
See“Climate Control Systems” in the
Index.
For more information about carbon
monoxide, see Engine Exhaust 0238.
Towing a trailer requires experience. The
combination of the vehicle and trailer is
longer and not as responsive as the vehicle
itself. Get used to the handling and braking
of the combination by driving on a level
road surface before driving on public roads.
The trailer structure, the tires, and the
brakes must all be rated to carry the
intended cargo. Inadequate trailer
equipment can cause the combination to
operate in an unexpected or unsafe manner.
Before driving, inspect all trailer hitch parts and attachments, safety chains, electrical
connectors, lamps, tires, and mirrors. See
Towing Equipment
0296. If the trailer has
electric brakes, start the combination
moving and then manually apply the trailer
brake controller to check that the trailer
brakes work. During the trip, occasionally
check that the cargo and trailer are secure
and that the lamps and any trailer brakes
are working.Towing with a Stability Control System
When towing, the stability control system
might be heard. The system reacts to
vehicle movement caused by the trailer,
which mainly occurs during cornering. This is
normal when towing heavier trailers.
Following Distance
Stay at least twice as far behind the vehicle
ahead as you would when driving without a
trailer. This can help to avoid heavy braking
and sudden turns.
Passing
More passing distance is needed when
towing a trailer. The combination of the
vehicle and trailer will not accelerate as
quickly and is much longer than the vehicle
alone. It is necessary to go much farther beyond the passed vehicle before returning
to the lane. Pass on level roadways. Avoid
passing on hills if possible.
Backing Up
Hold the bottom of the steering wheel with
one hand. To move the trailer to the left,
move that hand to the left. To move the
trailer to the right, move that hand to the
right. Always back up slowly and, if possible,
have someone guide you.
Making Turns
Caution
Turn more slowly and make wider arcs
when towing a trailer to prevent damage
to your vehicle. Making very sharp turns
could cause the trailer to contact the
vehicle.
Make wider turns than normal when towing,
so the trailer will not go over soft shoulders,
over curbs, or strike road signs, trees,
or other objects. Always signal turns well in
advance. Do not steer or brake suddenly.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
322 Vehicle Care
Jump Starting
Jump Starting - North America . . . . . . . . 391
Towing the Vehicle
Towing the Vehicle . . . . . . . . . . . . . . . . . . . . 394
Recreational Vehicle Towing . . . . . . . . . . . 395
Appearance Care
Exterior Care . . . . . . . . . . . . . . . . . . . . . . . . . . 398
Interior Care . . . . . . . . . . . . . . . . . . . . . . . . . . 403
Floor Mats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
General Information
For service and parts needs, visit your
dealer. You will receive genuine GM parts
and GM-trained and supported service
people.
Genuine GM parts have one of these marks:
California Proposition 65 Warning
{Warning
Most motor vehicles, including this one,
as well as many of its service parts and
fluids, contain and/or emit chemicals
known to the State of California to cause(Continued)
Warning (Continued)
cancer and birth defects or other
reproductive harm. Engine exhaust, many
parts and systems, many fluids, and
some component wear by-products
contain and/or emit these chemicals. For
more information go to
www.P65Warnings.ca.gov/
passenger-vehicle.
See Battery - North America 0343 and
Jump Starting - North America 0391 and the
back cover.
California Perchlorate Materials
Requirements
Certain types of automotive applications,
such as airbag initiators, seat belt
pretensioners, and lithium batteries
contained in electronic keys, may contain
perchlorate materials. Perchlorate Material –
special handling may apply. See
www.dtsc.ca.gov/hazardouswaste/
perchlorate.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Service and Maintenance 411
missing boots, loose or missing boot
clamps, center bearing excessive
looseness, missing or loose fasteners.
.Check restraint system components. See
Safety System Check060.
.Visually inspect fuel system for damage
or leaks.
.Visually inspect exhaust system and
nearby heat shields for loose or damaged
parts.
.Lubricate body components. See Exterior
Care 0398.
.Check starter switch. See Starter Switch
Check 0347.
.Check automatic transmission shift lock
control function. See Automatic
Transmission Shift Lock Control Function
Check 0347.
.Check ignition transmission lock. See
Ignition Transmission Lock Check 0347.
.Check parking brake and automatic
transmission park mechanism. See Park
Brake and P (Park) Mechanism Check
0 347.
.Check accelerator pedal for damage, high
effort, or binding. Replace if needed.
.Visually inspect gas strut for signs of
wear, cracks, or other damage. Check the
hold open ability of the strut. If the hold
open is low, service the gas strut. See Gas
Strut(s) 0349.
.Inspect sunroof track and seal,
if equipped. See Sunroof043.
.Verify spare tire key lock operation and
lubricate as needed. See Tire Changing
0 381.
.Visually inspect the spare tire to ensure
that it is tightly stowed under the vehicle.
Push, pull, and try to turn the tire. If the
spare tire moves, tighten as necessary.
See Tire Changing 0381.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./Cana-
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Index 449
Assistance Program, Roadside . . . . . . . . . . . . .431
Assistance Systems for Driving . . . . . . . . . . 274
Assistance Systems for Parking andBacking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
Audio Bluetooth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
Auto Stop
Stop/Start System . . . . . . . . . . . . . . . . . . . . . 233
Automatic Dimming Mirrors . . . . . . . . . . . . . . . . . . . . . . . 37
Door Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Emergency Braking (AEB) . . . . . . . . . . . . . . 277
Headlamp System . . . . . . . . . . . . . . . . . . . . . 142
Transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
Transmission Fluid . . . . . . . . . . . . . . . . . . . . . 333
Automatic Transmission
Manual Mode . . . . . . . . . . . . . . . . . . . . . . . . . 241
Shift Lock Control Function Check . . . . . . 347
Auxiliary Roof Mounted Lamp . . . . . . . . . . . . . . . . . . . 144
Auxiliary Jack . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Avoiding Untrusted Media Devices . . . . . . . .158
Axle, Front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
Axle, Rear . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346B
Battery
Exterior Lighting Battery Saver . . . . . . . . 147
Load Management . . . . . . . . . . . . . . . . . . . . . 146
Power Protection . . . . . . . . . . . . . . . . . . . . . . 147
Battery - North America . . . . . . . . . . . . .343, 391
Blade Replacement, Wiper . . . . . . . . . . . . . . . 348
Blind Spot Mirrors . . . . . . . . . . . . . . . . . . . . . . . . .37
Bluetooth Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 180, 181
Bluetooth Audio . . . . . . . . . . . . . . . . . . . . . . . . . 162
Brake Electric Boost . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Parking, Electric . . . . . . . . . . . . . . . . . . . . . . . . 247
System Warning Light . . . . . . . . . . . . . . . . . . 117
Brake Pad Life System . . . . . . . . . . . . . . . . . . . 342
Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .341 Antilock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
Assist . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
Pad Life System . . . . . . . . . . . . . . . . . . . . . . . 342
Braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 Automatic Emergency (AEB) . . . . . . . . . . . 277
Braking System
Front Pedestrian (FPB) . . . . . . . . . . . . . . . . . 278
Break-In, New Vehicle . . . . . . . . . . . . . . . . . . . . 228 Bulb Replacement
Center High-Mounted Stoplamp
(CHMSL) and Cargo Lamp . . . . . . . . . . . . 352
Halogen Bulbs . . . . . . . . . . . . . . . . . . . . . . . . . 350
Headlamp Aiming . . . . . . . . . . . . . . . . . . . . . . 350
Headlamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
Headlamps, Front Turn Signal, Sidemarker, and Parking Lamps . . . . . . 350
License Plate Lamps . . . . . . . . . . . . . . . . . . . 352
Taillamps, Turn Signal, Stoplamps, and Back-up Lamps . . . . . . . . . . . . . . . . . . 351
Buying New Tires . . . . . . . . . . . . . . . . . . . . . . . . 376
C
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
California Perchlorate Materials Requirements . . . 322
California Proposition 65 Warning . . . . . . . . . . . . . . . . . . .322, 343, 391, Back Cover
Canadian Vehicle Owners . . . . . . . . . . . . . . . . . . .2
Capacities and Specifications . . . . . . . . . . . . . 424
Carbon Monoxide
Engine Exhaust . . . . . . . . . . . . . . . . . . . . . . . . 238
Tailgate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Winter Driving . . . . . . . . . . . . . . . . . . . . . . . . . 220
Cargo Tie-Downs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97