2021 GMC SIERRA SERVICE MODE

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Vehicle Care 321
Vehicle Care
General Information
General Information . . . . . . . . . . . . . . . . . . . 322
California Proposition 65 Warning . . . . . 322
California Perchlorate MaterialsRequirements . . . . . . . . . . . . . . . . . . . . . . . . 322
Accessories and Modifications . . . . . . . . . 323
Vehicle Checks
Doing Your Own Service Work . . . . . . . . . 323
Hood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
Engine Compartment Overview . . . . . . . . 325
Engine Oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
Engine Oil Life System . . . . . . . . . . . . . . . . . 332
Automatic Transmission Fluid . . . . . . . . . . 333
Engine Air Filter Life System . . . . . . . . . . . 333
Engine Air Cleaner/Filter . . . . . . . . . . . . . . . 334
Cooling System . . . . . . . . . . . . . . . . . . . . . . . . 335
Engine Overheating . . . . . . . . . . . . . . . . . . . 338
Overheated Engine Protection Operating Mode . . . . . . . . . . . . . . . . . . . . . 340
Engine Fan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
Washer Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . 340
Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 341
Brake Pad Life System . . . . . . . . . . . . . . . . . 342
Brake Fluid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
Battery - North America . . . . . . . . . . . . . . . 343 Four-Wheel Drive . . . . . . . . . . . . . . . . . . . . . . 346
Front Axle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
Rear Axle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 346
Starter Switch Check . . . . . . . . . . . . . . . . . . 347
Automatic Transmission Shift Lock
Control Function Check . . . . . . . . . . . . . . 347
Ignition Transmission Lock Check . . . . . . 347
Park Brake and P (Park) Mechanism Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
Wiper Blade Replacement . . . . . . . . . . . . . 348
Glass Replacement . . . . . . . . . . . . . . . . . . . . 348
Windshield Replacement . . . . . . . . . . . . . . 348
Gas Strut(s) . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
Headlamp Aiming
Front Headlamp Aiming . . . . . . . . . . . . . . . 350
Bulb Replacement
Bulb Replacement . . . . . . . . . . . . . . . . . . . . . 350
Halogen Bulbs . . . . . . . . . . . . . . . . . . . . . . . . . 350
LED Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
Headlamps, Front Turn Signal, Sidemarker, and Parking Lamps . . . . . . 350
Taillamps, Turn Signal, Stoplamps, and Back-Up Lamps . . . . . . . . . . . . . . . . . . . . . . . 351
Center High-Mounted Stoplamp (CHMSL) and Cargo Lamp . . . . . . . . . . . . 352
License Plate Lamp . . . . . . . . . . . . . . . . . . . . 352
Electrical System
Electrical System Overload . . . . . . . . . . . . . 352
Fuses and Circuit Breakers . . . . . . . . . . . . . 353
Engine Compartment Fuse Block . . . . . . . 353
Instrument Panel Fuse Block (Left) . . . . . 357
Instrument Panel Fuse Block (Right) . . . 358
Wheels and Tires
Tires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
All-Season Tires . . . . . . . . . . . . . . . . . . . . . . . . 361
Winter Tires . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
All-Terrain Tires . . . . . . . . . . . . . . . . . . . . . . . 362
Tire Sidewall Labeling . . . . . . . . . . . . . . . . . 362
Tire Designations . . . . . . . . . . . . . . . . . . . . . . 364
Tire Terminology and Definitions . . . . . . 365
Tire Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . 367
Tire Pressure Monitor System . . . . . . . . . 368
Tire Pressure Monitor Operation . . . . . . 369
Tire Inspection . . . . . . . . . . . . . . . . . . . . . . . . . 373
Tire Rotation . . . . . . . . . . . . . . . . . . . . . . . . . . 374
When It Is Time for New Tires . . . . . . . . 375
Buying New Tires . . . . . . . . . . . . . . . . . . . . . 376
Different Size Tires and Wheels . . . . . . . . 377
Uniform Tire Quality Grading . . . . . . . . . . 377
Wheel Alignment and Tire Balance . . . . 378
Wheel Replacement . . . . . . . . . . . . . . . . . . . 378
Tire Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
If a Tire Goes Flat . . . . . . . . . . . . . . . . . . . . . 380
Tire Changing . . . . . . . . . . . . . . . . . . . . . . . . . . 381
Full-Size Spare Tire . . . . . . . . . . . . . . . . . . . . 390

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Vehicle Care 337
Check to see if coolant is visible in the
coolant surge tank. If the coolant inside the
coolant surge tank is boiling, wait until it
cools down. The coolant level should be at
or above the indicated mark. If it is not,
there may be a leak in the cooling system.
If coolant is visible but the coolant level is
not at or above the indicated mark, see the
following sections on how to add coolant to
the coolant surge tank following.
Automatic Coolant Service Fill
Instructions (L3B Engine)
This feature assists in filling and removing
air from the cooling system after service of
components or when coolant is added after
being too low.
To activate the fill and air removal process:1. Remove the coolant surge tank pressure cap when the cooling system, including
the coolant surge tank pressure cap and
upper radiator hose, is no longer hot.
Turn the pressure cap; slowly
counterclockwise about one full turn. If a
hiss is heard, wait for that to stop.
A hiss means there is still some
pressure left. 2. Keep turning the pressure cap slowly,
and remove it.
3. Fill the coolant surge tank with the proper mixture to the indicated mark.
4. Connect the vehicle to a battery charger.
5. Set the ignition to service mode, see Ignition Positions (Keyless Access) 0230
or
Ignition Positions (Key Access) 0229.
6. Turn off the air conditioning.
7. Set the parking brake.
8. At the same time, press the accelerator and the brake for automatic vehicles for
two seconds, then release.
9. Listen for pump activation and movement of the control valves while
watching the level of the coolant in the
surge tank. Add fluid as the level drops
below the indicated mark on the surge
tank. Allow 15 minutes for the fill and air
removal process to complete.
10. Reinstall the surge tank cap.
If the tank empties, turn the ignition off,
allow the Electronic Control Module (ECM) to
go to sleep, about two minutes, refill to the
indicated mark, and repeat Steps 5–9.
How to Add Coolant to the Coolant
Surge Tank for Gasoline Engines
Except L3B
If the vehicle has a diesel engine, see
“Cooling System” in the Duramax diesel
supplement for the proper coolant fill
procedure.
{Warning
Spilling coolant on hot engine parts can
burn you. Coolant contains ethylene
glycol and it will burn if the engine parts
are hot enough.
{Warning
Plain water, or other liquids such as
alcohol, can boil before the proper
coolant mixture will. With plain water or
the wrong mixture, the engine could get
too hot but there would not be an
overheat warning. The engine could catch
fire and you or others could be burned.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
340 Vehicle Care
If there is still no sign of steam and the
vehicle is equipped with an engine driven
cooling fan, push down the accelerator until
the engine speed is about twice as fast as
normal idle speed for at least five minutes
while the vehicle is parked. If the warning is
still there, turn off the engine and get
everyone out of the vehicle until it
cools down.
If there is no sign of steam, idle the engine
for five minutes while parked. If the warning
is still displayed, turn off the engine until it
cools down.
Overheated Engine Protection
Operating Mode
If an overheated engine condition exists and
the ENGINE POWER IS REDUCED message
displays, an overheat protection mode which
alternates firing groups of cylinders helps to
prevent engine damage. In this mode, a loss
in power and engine performance will be
noticed. This operating mode allows the
vehicle to be driven to a safe place in an
emergency. Driving extended distances and/
or towing a trailer in the overheat
protection mode should be avoided.If the engine or transmission detects an
impending hot fluid condition, then the
transmission may force upshifts to limit
temperatures. Downshifts may also be
prevented in this instance. Normal operation
may continue unless the display indicates
there is a hot condition and engine should
be idled.
Caution
After driving in the overheated engine
protection operating mode, the engine oil
will be severely degraded. Any repairs
performed before the engine is cool may
cause engine damage. Allow the engine
to cool before attempting any repair.
Repair the cause of coolant loss, change
the oil, and reset the oil life system. See
Engine Oil
0330.
Engine Fan
If the vehicle has the Duramax diesel
engine, see the Duramax diesel supplement.
The vehicle has electric cooling fan(s). The
fans may be heard spinning at low speed
during most everyday driving. The fans may
turn off if no cooling is required. Under
heavy vehicle loading, trailer towing, high outside temperatures, or operation of the air
conditioning system, the fans may change
to high speed and an increase in fan noise
may be heard. This is normal and indicates
that the cooling system is functioning
properly. The fans will change to low speed
when additional cooling is no longer
required.
The electric engine cooling fans may run
after the engine has been turned off. This is
normal and no service is required.
Washer Fluid
What to Use
When windshield washer fluid needs to be
added, be sure to read the manufacturer's
instructions before use. Use a fluid that has
sufficient protection against freezing in an
area where the temperature may fall below
freezing.
Adding Washer Fluid
The vehicle has a low washer fluid message
on the DIC that comes on when the washer
fluid is low. The message is displayed for
15 seconds at the start of each ignition cycle.
When the WASHER FLUID LOW ADD FLUID

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
372 Vehicle Care
4. If the vehicle has an uplevel DIC, use theDIC controls on the right side of the
steering wheel to scroll to the Tire
Pressure screen under the DIC info page.
If the vehicle has a base level DIC, use
the trip odometer reset stem to scroll to
the Tire Pressure screen.
5. If the vehicle has an uplevel DIC, press and hold the thumbwheel located in the
center of the DIC controls on the right
side of the steering wheel.
If the vehicle has a base level DIC, press
and hold the trip odometer reset stem
for about five seconds. A message asking
if the process should begin should
appear. Select yes and press the trip
odometer reset stem to confirm the
selection.
The horn sounds twice to signal the
receiver is in relearn mode and the TIRE
LEARNING ACTIVE message displays on
the DIC screen.
6. Start with the driver side front tire.
7. Place the relearn tool against the tire sidewall, near the valve stem. Then press
the button to activate the TPMS sensor.
A horn chirp confirms that the sensor
identification code has been matched to
this tire and wheel position. 8. Proceed to the passenger side front tire,
and repeat the procedure in Step 7.
9. Proceed to the passenger side rear tire, and repeat the procedure in Step 7.
10. Proceed to the driver side rear tire, and repeat the procedure in Step 7. The horn
sounds two times to indicate the sensor
identification code has been matched to
the driver side rear tire, and the TPMS
sensor matching process is no longer
active. The TIRE LEARNING ACTIVE
message on the DIC display screen
goes off.
11. Turn the vehicle off.
12. Set all four tires to the recommended air pressure level as indicated on the Tire
and Loading Information label.
Trailer Tire Pressure Monitoring
Operation
If equipped, the Trailer Tire Pressure
Monitoring System (TTPMS) is designed to
monitor the pressure of the trailer tires and
warn the driver when a low pressure
condition exists. TTPMS sensors for four tires
are provided. The system can accommodate
a trailer with up to six tires if additional sensors are purchased from the dealer. Also,
the system can be paired with up to five
individual trailers.
Prior to use, the vehicle must learn the
sensors by following the learning process.
See
Trailering App 0307.
Contact your trailer service center or tire
service center to have the pressure sensors
installed inside the trailer tires. The
technician should insert the sensor stem
through the hole in the trailer wheel. When
the sensor is correctly positioned, the nut on
the sensor stem should be tightened to
8Y (6 lb ft). When mounting the trailer
tire onto the trailer wheel be careful not to
damage the sensor.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Technical Data 423
Technical Data
Vehicle Identification
Vehicle Identification Number (VIN) . . . 423
Service Parts Identification . . . . . . . . . . . . 423
Vehicle Data
Capacities and Specifications . . . . . . . . . . 424
Engine Drive Belt Routing . . . . . . . . . . . . . 427
Vehicle Identification
Vehicle Identification
Number (VIN)
This legal identifier is in the front corner of
the instrument panel, on the driver side of
the vehicle. It can be seen through the
windshield from outside. The Vehicle
Identification Number (VIN) also appears on
the Vehicle Certification label and certificates
of title and registration.
Engine Identification
The eighth character in the VIN is the
engine code. This code identifies the
vehicle's engine, specifications, and
replacement parts. See“Engine
Specifications” underCapacities and
Specifications 0424 for the vehicle's
engine code.
Service Parts Identification
There may be a large barcode on the
certification label on the center pillar that
you can scan for the following information:
.Vehicle Identification Number (VIN)
.Model designation
.Paint information
.Production options
If there is not a large barcode on this label,
then you will find this same information on
a label inside of the glove box.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Customer Information 431
I:View service records from your
dealership and add your own.
D: Select a dealer and view locations,
maps, phone numbers, and hours.
r: Track your vehicle’s warranty
information.
J: View active recalls by Vehicle
Identification Number (VIN). See Vehicle
Identification Number (VIN) 0423.
H:Manage your profile and payment
information. View your GM Rewards Card
earnings and My GMC Rewards points.
F: Chat live with online help
representatives.
Visit my.gmc.com and create an account
today.
GMC Owner Centre (Canada)
mygmccanada.ca
Visit the GMC Owner Centre at
mygmccanada.ca (English) or
my.gmccanada.ca (French) to access similar
benefits to the U.S. site.
GM Mobility Reimbursement
Program
This program is available to qualified
applicants for cost reimbursement, up to
certain limits, of eligible aftermarket
adaptive equipment required for the vehicle,
such as hand controls or a wheelchair/
scooter lift for the vehicle.
To learn about the GM Mobility program,
see www.gmmobility.com or call the GM
Mobility Assistance Center at 1-800-323-9935.
Text Telephone (TTY) users, call
1-800-833-9935.
General Motors of Canada also has a
Mobility program. See www.gm.ca, or call
1-800-GM-DRIVE (800-463-7483) for details.
TTY users call 1-800-263-3830.
Roadside Assistance Program
For U.S.-purchased vehicles, call
1-888-881-3302; (Text Telephone (TTY):
1-888-889-2438).
For Canadian-purchased vehicles, call
1-800-268-6800.
Service is available 24 hours a day, 365 days
a year.
Calling for Assistance
When calling Roadside Assistance, have the
following information ready:
.Your name, home address, and home
telephone number
.Telephone number of your location
.Location of the vehicle
.Model, year, color, and license plate
number of the vehicle
.Odometer reading, Vehicle Identification
Number (VIN), and delivery date of the
vehicle
.Description of the problem
Coverage
Services are provided for the duration of the
vehicle's powertrain warranty.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Customer Information 435
coverage is not available from your current
insurance carrier, consider switching to
another insurance carrier.
If the vehicle is leased, the leasing company
may require you to have insurance that
ensures repairs with Genuine GM Original
Equipment Manufacturer (OEM) parts or
Genuine Manufacturer replacement parts.
Read the lease carefully, as you may be
charged at the end of the lease for poor
quality repairs.
If a Crash Occurs
If there has been an injury, call emergency
services for help. Do not leave the scene of
a crash until all matters have been taken
care of. Move the vehicle only if its position
puts you in danger, or you are instructed to
move it by a police officer.
Give only the necessary information to
police and other parties involved in the
crash.
For emergency towing seeRoadside
Assistance Program 0431.
Gather the following information:
.Driver name, address, and telephone
number
.Driver license number
.Owner name, address, and telephone
number
.Vehicle license plate number
.Vehicle make, model, and model year
.Vehicle Identification Number (VIN)
.Insurance company and policy number
.General description of the damage to the
other vehicle
Choose a reputable repair facility that uses
quality replacement parts. See “Collision
Parts” earlier in this section.
If the airbag has inflated, see What Will You
See after an Airbag Inflates? 065.
Managing the Vehicle Damage Repair
Process
In the event that the vehicle requires
damage repairs, GM recommends that you
take an active role in its repair. If you have
a pre-determined repair facility of choice,
take the vehicle there, or have it towed
there. Specify to the facility that any
required replacement collision parts be
original equipment parts, either new
Genuine GM parts or recycled original GM
parts. Remember, recycled parts will not be
covered by the GM vehicle warranty. Insurance pays the bill for the repair, but
you must live with the repair. Depending on
your policy limits, your insurance company
may initially value the repair using
aftermarket parts. Discuss this with the
repair professional, and insist on Genuine
GM parts. Remember, if the vehicle is
leased, you may be obligated to have the
vehicle repaired with Genuine GM parts,
even if your insurance coverage does not
pay the full cost.
If another party's insurance company is
paying for the repairs, you are not obligated
to accept a repair valuation based on that
insurance company's collision policy repair
limits, as you have no contractual limits
with that company. In such cases, you can
have control of the repair and parts choices
as long as the cost stays within reasonable
limits.
Publication Ordering Information
Service Manuals
Service manuals have the diagnosis and
repair information on the engine,
transmission, axle, suspension, brakes,
electrical system, steering system, body, etc.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
436 Customer Information
Customer Literature
Owner’s manuals are written specifically for
owners and are intended to provide basic
operational information about the vehicle.
The owner’s manual includes the
Maintenance Schedule for all models.
Customer literature publications available for
purchase include owner’s manuals, warranty
manuals, and portfolios. Portfolios include an
owner’s manual, warranty manual,
if applicable, and zip lock bag or pouch.
Current and Past Models
Service manuals and customer literature are
available for many current and past model
year GM vehicles.
To order, call 1-800-551-4123 Monday–Friday,
8:00 a.m.–6:00 p.m. eastern time
For credit card orders only (VISA,
MasterCard, or Discover), see Helm, Inc. at:
www.helminc.com.
To order by mail, write to:
Helm, Incorporated
Attention: Customer Service
47911 Halyard Drive
Plymouth, MI 48170
Make checks payable in U.S. funds.
Radio Frequency Statement
This vehicle uses license-exempt transmitters
/ receivers / systems that operate on a
radio frequency that complies with Part 15/
Part 18 of the Federal Communications
Commission (FCC) rules and with Innovation,
Science and Economic Development (ISED)
Canada's license-exempt RSS(s) / RSP-100 /
ICES-GEN.
Operation is subject to the following two
conditions:1. The device may not cause harmful interference.
2. The device must accept any interference received, including interference that may
cause undesired operation of the device.
Changes or modifications to any of these
systems by other than an authorized service
facility could void authorization to use this
equipment.
Reporting Safety Defects
Reporting Safety Defects to the
United States Government
If you believe that your vehicle has a
defect which could cause a crash or
could cause injury or death, you should
immediately inform the National
Highway Traffic Safety Administration
(NHTSA) in addition to notifying General
Motors.
If NHTSA receives similar complaints, it
may open an investigation, and if it
finds that a safety defect exists in a
group of vehicles, it may order a recall
and remedy campaign. However, NHTSA
cannot become involved in individual
problems between you, your dealer,
or General Motors.
To contact NHTSA, you may call the
Vehicle Safety Hotline toll-free at
1-888-327-4236 (TTY: 1-800-424-9153); go
to http://www.safercar.gov; or
write to: