2020 GMC SIERRA Electrical

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/10/19
Vehicle Care 423
6. Check that the jumper cablesdo not have loose or missing
insulation. If they do, you could
get a shock. The vehicles
could be damaged too.
Before you connect the cables,
here are some basic things you
should know. Positive (+) will
go to positive (+) or to a remote
positive (+) terminal if the
vehicle has one. Negative (−)
will go to a heavy, unpainted
metal engine part or to a
remote negative (−) terminal if
the vehicle has one.
Do not connect positive (+) to
negative (−) or you will get a
short that would damage the
battery and maybe other parts
too. And do not connect the
negative (−) cable to the
negative (−) terminal on the
dead battery because this can
cause sparks.
7. Connect one end of the red positive (+) cable to the remote
positive (+) terminal of the
vehicle with the discharged
battery. 8. Do not let the other end touch
metal. Connect it to the
positive (+) terminal of the
good battery. Use a remote
positive (+) terminal if the
vehicle has one.
9. Connect one end of the black negative (−) cable to the
negative (−) terminal of the
good battery. Use a remote
negative (−) terminal if the
vehicle has one.
Do not let the other end touch
anything until the next step.
10. Connect the other end of the negative (−) cable to the
remote negative (−) terminal to
the discharged battery.
11. Start the vehicle with the good battery and run the engine for a
while.
12. Try to start the vehicle that had the dead battery. If it will not
start after a few tries, it
probably needs service.Caution
If the jumper cables are
connected or removed in the
wrong order, electrical shorting
may occur and damage the
vehicle. The repairs would not be
covered by the vehicle warranty.
Always connect and remove the
jumper cables in the correct order,
making sure that the cables do
not touch each other or other
metal.
Jumper Cable Removal
Reverse the sequence exactly when
removing the jumper cables.
After starting the disabled vehicle
and removing the jumper cables,
allow it to idle for several minutes.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
450 Service and Maintenance
Additional
Maintenance and Care
Your vehicle is an important
investment and caring for it properly
may help to avoid future costly
repairs. To maintain vehicle
performance, additional
maintenance services may be
required.
It is recommended that your dealer
perform these services—their
trained dealer technicians know
your vehicle best. Your dealer can
also perform a thorough
assessment with a multi-point
inspection to recommend when your
vehicle may need attention.
The following list is intended to
explain the services and conditions
to look for that may indicate
services are required.
Battery
The 12-volt battery supplies power
to start the engine and operate any
additional electrical accessories. .
To avoid break-down or failure to
start the vehicle, maintain a
battery with full cranking power.
. Trained dealer technicians have
the diagnostic equipment to test
the battery and ensure that the
connections and cables are
corrosion-free.
Belts
. Belts may need replacing if they
squeak or show signs of
cracking or splitting.
. Trained dealer technicians have
access to tools and equipment
to inspect the belts and
recommend adjustment or
replacement when necessary.
Brakes
Brakes stop the vehicle and are
crucial to safe driving.
. Signs of brake wear may include
chirping, grinding, or squealing
noises, or difficulty stopping. .
Trained dealer technicians have
access to tools and equipment
to inspect the brakes and
recommend quality parts
engineered for the vehicle.
Fluids
Proper fluid levels and approved
fluids protect the vehicle’s systems
and components. See
Recommended Fluids and
Lubricants 0453 for GM approved
fluids.
. Engine oil and windshield
washer fluid levels should be
checked at every fuel fill.
. Instrument cluster lights may
come on to indicate that fluids
may be low and need to be
filled.
Hoses
Hoses transport fluids and should
be regularly inspected to ensure
that there are no cracks or leaks.
With a multi-point inspection, your
dealer can inspect the hoses and
advise if replacement is needed.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
472 Customer Information
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.
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, infotainment manuals, and
portfolios. Portfolios include an
owner ’s manual, warranty manual,
infotainment 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 has systems that
operate on a radio frequency that
complies with Part 15/Part 18 of the
Federal Communications
Commission (FCC) rules and with

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
OnStar 477
OnStar
OnStar Overview
OnStar Overview . . . . . . . . . . . . . 477
OnStar Services
Emergency . . . . . . . . . . . . . . . . . . . 478
Security . . . . . . . . . . . . . . . . . . . . . . 479
OnStar Additional Information
OnStar AdditionalInformation . . . . . . . . . . . . . . . . . . 479
OnStar Overview
=Voice Command Button
QBlue OnStar Button
>Red Emergency Button
This vehicle may be equipped with a
comprehensive, in-vehicle system
that can connect to an OnStar
Advisor for Emergency, Security,
Navigation, Connections, and
Diagnostics Services. OnStar
services may require a paid service
plan and data plan. OnStar requires
the vehicle battery and electrical
system, cellular service, and GPS
satellite signals to be available and
operating. OnStar acts as a link to
existing emergency service
providers. OnStar may collect
information about you and your
vehicle, including location
information. See OnStar User Terms, Privacy Statement, and
Software Terms for more details
including system limitations at
www.onstar.com (U.S.) or
www.onstar.ca (Canada).
The OnStar system status light is
next to the OnStar buttons. If the
status light is:
.
Solid Green: System is ready.
. Flashing Green: On a call.
. Red: Indicates a problem.
. Off: System is off. Press
Q
twice to speak with an OnStar
Advisor.
Press
Qor call 1-888-4ONSTAR
(1-888-466-7827) to speak to an
Advisor.
Functionality of the Voice Command
button may vary by vehicle and
region.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
480 OnStar
.PressQto speak with an
Advisor.
OnStar or connected services
cannot work unless the vehicle is in
a place where OnStar has an
agreement with a wireless service
provider for service in that area. The
wireless service provider must also
have coverage, network capacity,
reception, and technology
compatible with OnStar or
connected services. Service
involving location information about
the vehicle cannot work unless GPS
signals are available, unobstructed,
and compatible with the OnStar
hardware. OnStar or connected
services may not work if the OnStar
equipment is not properly installed
or it has not been properly
maintained. If equipment or software
is added, connected, or modified,
OnStar or connected services may
not work. Other problems beyond
the control of OnStar —such as
hills, tall buildings, tunnels, weather,
electrical system design and
architecture of the vehicle, damage to the vehicle in a crash, or wireless
phone network congestion or
jamming
—may prevent service.
See Radio Frequency Statement
0 472.
Services for People with
Disabilities
Advisors provide services to help
with physical disabilities and
medical conditions.
Press
Qto help:
. Locate a gas station with an
attendant to pump gas.
. Find a hotel, restaurant, etc.,
that meets accessibility needs.
. Provide directions to the closest
hospital or pharmacy in urgent
situations.
TTY Users
OnStar has the ability to
communicate to deaf,
hard-of-hearing, or speech-impaired
customers while in the vehicle. The
available dealer-installed TTY
system can provide in-vehicle access to all OnStar services,
except Virtual Advisor and OnStar
Turn-by-Turn Navigation.
If equipped, TTY mode can be
turned on or off by touching
Settings, then Apps, and then
Phone. When TTY mode is on,
phone calls can be made or
received with OnStar using the
infotainment display.
OnStar Personal Identification
Number (PIN)
A PIN is needed to access some
OnStar services. The PIN will need
to be changed the first time when
speaking with an Advisor. To
change the OnStar PIN, contact an
OnStar Advisor by pressing
Qor
calling 1-888-4ONSTAR.
Warranty
OnStar equipment may be
warranted as part of the vehicle
warranty.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-13337776) - 2020 - CRC - 4/4/19
OnStar 481
Languages
The vehicle can be programmed to
respond in multiple languages.
Press
Qand ask for an Advisor.
Advisors are available in English,
Spanish, and French. Available
languages may vary by country.
Potential Issues
OnStar cannot perform Remote
Door Unlock or Stolen Vehicle
Assistance after the vehicle has
been off continuously for 10 days
without an ignition cycle. If the
vehicle has not been started for
10 days, OnStar can contact
Roadside Assistance or a locksmith
to help gain access to the vehicle.
Global Positioning
System (GPS)
. Obstruction of the GPS can
occur in a large city with tall
buildings; in parking garages;
around airports; in tunnels and
underpasses; or in an area with
very dense trees. If GPS signals
are not available, the OnStar
system should still operate to call OnStar. However, OnStar
could have difficulty identifying
the exact location.
. In emergency situations, OnStar
can use the last stored GPS
location to send to emergency
responders.
A temporary loss of GPS can cause
loss of the ability to send a
Turn-by-Turn Navigation route. The
Advisor may give a verbal route or
may ask for a call back after the
vehicle is driven into an open area.
Cellular and GPS Antennas
Cellular reception is required for
OnStar to send remote signals to
the vehicle. Do not place items over
or near the antenna to prevent
blocking cellular and GPS signal
reception.
Unable to Connect to OnStar
Message
If there is limited cellular coverage
or the cellular network has reached
maximum capacity, this message may come on. Press
Qto try the
call again or try again after driving a
few miles into another cellular area.
Vehicle and Power Issues
OnStar services require a vehicle
electrical system, wireless service,
and GPS satellite technologies to be
available and operating for features
to function properly. These systems
may not operate if the battery is
discharged or disconnected.
Add-on Electrical Equipment
The OnStar system is integrated
into the electrical architecture of the
vehicle. Do not add any electrical
equipment. See Add-On Electrical
Equipment 0322. Added electrical
equipment may interfere with the
operation of the OnStar system and
cause it to not operate.
Vehicle Software Updates
OnStar or GM may remotely deliver
software updates or changes to the
vehicle without further notice or
consent. These updates or changes
may enhance or maintain safety,

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/-
Mexico-13337776) - 2020 - CRC - 4/4/19
488 Index
IndexA
Accessories andModifications . . . . . . . . . . . . . . . . . . 329
Accessory Power . . . . . . . . . . . . . . . 217
Active Fuel Management . . . . . . . 219
Adaptive Cruise Control . . . . . . . . 245
Add-On Electrical Equipment . . . 322
Adding a Snow Plow or Similar Equipment . . . . . . . . . . . . . 323
Additional Information
OnStar . . . . . . . . . . . . . . . . . . . . . . . 479
Additional Maintenance and Care . . . . . . . . . . . . . . . . . . . . . . 450
Adjustments
Lumbar, Front Seats . . . . . . . . . . . . 57
Air Cleaner/Filter, Engine . . . . . . . 344
Air Conditioning . . . . . . . . . . . 177, 179
Air Filter Life System . . . . . . . . . . . . . . . . . . . 343
Air Filter, Passenger Compartment . . . . . . . . . . . . . . . . . 183
Air Vents . . . . . . . . . . . . . . . . . . . . . . . 182
Airbag System Check . . . . . . . . . . . . . . . . . . . . . . . . . . 84
How Does an Airbag
Restrain? . . . . . . . . . . . . . . . . . . . . . 77
Passenger Sensing System . . . . 78 Airbag System (cont'd)
What Makes an Airbag
Inflate? . . . . . . . . . . . . . . . . . . . . . . . . 76
What Will You See after an
Airbag Inflates? . . . . . . . . . . . . . . . 77
When Should an Airbag Inflate? . . . . . . . . . . . . . . . . . . . . . . . . 76
Where Are the Airbags? . . . . . . . . 74
Airbags
Adding Equipment to theVehicle . . . . . . . . . . . . . . . . . . . . . . . . 83
Passenger Status Indicator . . . 137
Readiness Light . . . . . . . . . . . . . . 136
Servicing Airbag-Equipped Vehicles . . . . . . . . . . . . . . . . . . . . . . . 83
System Check . . . . . . . . . . . . . . . . . . 72
Alarm Vehicle Security . . . . . . . . . . . . . . . . 37
Alert Lane Change . . . . . . . . . . . . . . . . . 274
Side Blind Zone (SBZA) . . . . . . 274
All-Season Tires . . . . . . . . . . . . . . . . 379
All-Terrain Tires . . . . . . . . . . . . . . . . . 381
Antilock Brake System (ABS) . . . 232 Warning Light . . . . . . . . . . . . . . . . . 141
Appearance Care Exterior . . . . . . . . . . . . . . . . . . . . . . . 429
Interior . . . . . . . . . . . . . . . . . . . . . . . . 435

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/-
Mexico-13337776) - 2020 - CRC - 4/4/19
Index 491
DiagnosticsConnected Services . . . . . . . . . . 487
Differential, Limited-Slip . . . . . . . . 242
Distracted Driving . . . . . . . . . . . . . . . 187
Dome Lamps . . . . . . . . . . . . . . . . . . . 172
Door Ajar Light . . . . . . . . . . . . . . . . . . . . . 148
Delayed Locking . . . . . . . . . . . . . . . . 26
Locks . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Power Locks . . . . . . . . . . . . . . . . . . . . 26
Drive Belt Routing, Engine . . . . . . 462
Driver Assistance Systems . . . . . 256
Driver Information
Center (DIC) . . . . . . . . . . . . . 148, 149
Driver Mode Control . . . . . . . . . . . . 238
Driver Mode Control Light . . . . . . 145
Driving Assistance Systems . . . . . . . . . . 268
Better Fuel Economy . . . . . . . . . 186
Characteristics andTowing Tips . . . . . . . . . . . . . . . . . 287
Defensive . . . . . . . . . . . . . . . . . . . . . 187
Drunk . . . . . . . . . . . . . . . . . . . . . . . . . 188
Hill and Mountain Roads . . . . . . 197
If the Vehicle is Stuck . . . . . . . . . 199
Loss of Control . . . . . . . . . . . . . . . 190
Off-Road . . . . . . . . . . . . . . . . . . . . . 191
Off-Road Recovery . . . . . . . . . . . 190 Driving (cont'd)
Vehicle Load Limits . . . . . . . . . . . 200
Wet Roads . . . . . . . . . . . . . . . . . . . 196
Winter . . . . . . . . . . . . . . . . . . . . . . . . 197
Dual Automatic Climate Control System . . . . . . . . . . . . . . . . 179
E
E85 or FlexFuel . . . . . . . . . . . . . . . . 282
Electric Brake Boost . . . . . . . . . . . . 232
Electric Parking Brake . . . . . . . . . . 233
Electric Parking Brake Light . . . . 141
Electrical Equipment,Add-On . . . . . . . . . . . . . . . . . . . . . . . 322
Electrical System Engine Compartment FuseBlock . . . . . . . . . . . . . . . . . . . . . . . . 371
Fuses and Circuit Breakers . . . 370
Instrument Panel Fuse Block . . . . . . . . . . . . . . . . . . . 374, 376
Overload . . . . . . . . . . . . . . . . . . . . . 370
Electronic Stability Control (ESC) Off Light . . . . . . . . . . . . . . . . 144
Emergency
OnStar . . . . . . . . . . . . . . . . . . . . . . . 478
Engine Air Cleaner/Filter . . . . . . . . . . . . . 344 Engine (cont'd)
Check Light (Malfunction
Indicator) . . . . . . . . . . . . . . . . . . . . 138
Compartment Overview . . . . . . . 332
Coolant Temperature
Gauge . . . . . . . . . . . . . . . . . . . . . . 134
Coolant Temperature Warning Light . . . . . . . . . . . . . . . 145
Cooling System . . . . . . . . . . . . . . . 346
Drive Belt Routing . . . . . . . . . . . . 462
Exhaust . . . . . . . . . . . . . . . . . . . . . . 220
Fan . . . . . . . . . . . . . . . . . . . . . . . . . . . 353
Heater . . . . . . . . . . . . . . . . . . . . . . . . 215
Oil Life System . . . . . . . . . . . . . . . 341
Oil Pressure Gauge . . . . . . . . . . 133
Oil Pressure Light . . . . . . . . . . . . 146
Overheated Protection Operating Mode . . . . . . . . . . . . . 352
Overheating . . . . . . . . . . . . . . . . . . 351
Power Messages . . . . . . . . . . . . . 156
Running While Parked . . . . . . . . 220
Starting . . . . . . . . . . . . . . . . . . . . . . . 212
Engine Air Filter Life System . . . . 343
Entry Lighting . . . . . . . . . . . . . . . . . . . 173
Equipment, Towing . . . . . . . . . . . . . 296
Event Data Recorders . . . . . . . . . . 475
Exit Lighting . . . . . . . . . . . . . . . . . . . . 173
Extended Parking . . . . . . . . . . . . . . . 219