2021 GMC SIERRA brakes

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 293
Trailer Towing
If equipped with a diesel engine, see the
Duramax diesel supplement.
Caution
Towing a trailer improperly can damage
the vehicle and result in costly repairs
not covered by the vehicle warranty. To
tow a trailer correctly, follow the
directions in this section and see your
dealer for important information about
towing a trailer with the vehicle.
Trailering is different than just driving the
vehicle by itself. Trailering means changes in
handling, acceleration, braking, durability,
and fuel economy. Successful, safe trailering
takes correct equipment, and it has to be
used properly.
The following information has many
time-tested, important trailering tips and
safety rules. Many of these are important
for your safety and that of your passengers.
Read this section carefully before pulling a
trailer.
Trailer Weight
{Warning
Never exceed the towing capacity for
your vehicle.
Safe trailering requires monitoring the
weight, speed, altitude, road grades, outside
temperature, and how frequently the vehicle
is used to tow a trailer.
Trailer Weight Ratings
When towing a trailer, the combined weight
of the vehicle, vehicle contents, trailer, and
trailer contents must be below all of the
maximum weight ratings for the vehicle,
including:
.GCWR: Gross Combined Weight Rating
.GVWR: Gross Vehicle Weight Rating
.Maximum Trailer Weight Rating
.GAWR-RR: Gross Axle Weight Rating-Rear
.Maximum Trailer Tongue Weight Rating
See “Weight-Distributing Hitch and
Adjustment” underTowing Equipment 0296
to determine if equalizer bars are required
to obtain the maximum trailer weight
rating. See
“Trailer Brakes” underTowing
Equipment 0296 to determine if brakes are
required based on your trailer's weight.
The only way to be sure the weight is not
exceeding any of these ratings is to weigh
the tow vehicle and trailer combination,
fully loaded for the trip, getting individual
weights for each of these items.
A trailering information label on the B-pillar
shows tow rating information for the
vehicle.
{Warning
You and others could be seriously injured
or killed if the trailer is too heavy or the
trailer brakes are inadequate for the load.
The vehicle may be damaged, and the
repairs would not be covered by the
vehicle warranty.
Only tow a trailer if all the steps in this
section have been followed. Ask your
dealer for advice and information about
towing a trailer.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
300 Driving and Operating
Trailer Brakes
Loaded trailers over 900 kg (2,000 lb) must
be equipped with brake systems and with
brakes for each axle. Trailer braking
equipment conforming to Canadian
Standards Association (CSA) requirement
CAN3-D313, or its equivalent, is
recommended.
State or local regulations may require
trailers to have their own braking system if
the loaded weight of the trailer exceeds
certain minimums that can vary from state
to state. Read and follow the instructions for
the trailer brakes so they are installed,
adjusted, and maintained properly. Never
attempt to tap into your vehicle's hydraulic
brake system. If you do, both the vehicle
antilock brakes and the trailer brakes may
not function, which could result in a crash.
Auxiliary Battery
If equipped, the vehicle's auxiliary battery
can be used to supply electrical power to
additional equipment that may be added,
such as a slide-in camper.Locate the auxiliary battery connector under
the hood on the driver side of the vehicle,
next to the engine compartment fuse block.
Follow the proper installation instructions
included with any electrical equipment that
is installed.
Caution
To prevent draining the auxiliary battery,
always turn off electrical equipment
when not in use and do not use any
equipment that may exceed the
maximum amperage rating of 30 amps.
Trailer Wiring Harness
Basic Trailer Wiring
If the vehicle is not equipped with a trailer
connector on the rear bumper, a 7-wire
trailering harness is tied to the vehicles
frame. The harness requires the installation
of a trailer connector, which is available
through your dealer.
Use only a round, seven-wire connector with
flat blade terminals meeting SAE J2863
specifications for proper electrical
connectivity.The seven-wire harness contains the
following trailer circuits:
Stop/Turn
Signal Left Yellow/Blue
Stop/Turn Signal
Right Green/Violet
Tail/Parking Lamps Gray/Brown
Reverse Lamps White/Green
Battery Feed Red/Green
Ground White
Electric Trailer Brake Blue
If equipped, the trailer wiring harness, with
a 7-pin connector and a 4-pin connector, is
mounted on the vehicle's rear bumper.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 301
The trailer connectors contain the following
circuits.
1. Ground
2. Tail Lamps3. Left Turn/Brake
4. Right Turn/Brake
1. Left Turn/Brake
2. Tail Lamps
3. Reverse Lamps
4. Battery Feed
5. Right Turn/Brake
6. Electric Brakes
7. Ground
If equipped, trailering camera connectors are
available in the bumper trailer receptacle in
place of the four pin connector. The inside
trailer auxiliary camera should be installed on the top left hand side (A) and the rear
trailer auxiliary camera (B) should be
installed on the top right hand side.If equipped with the fifth wheel/ gooseneck
trailer package, the harness connector is
mounted on the inside of the pickup bed
behind the rear wheel.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 303
Tow/Haul Mode is most useful when towing
a heavy trailer or carrying a large or
heavy load:
.Through rolling terrain.
.In stop-and-go traffic.
.In busy parking lots.
Operating the vehicle in Tow/Haul Mode
when lightly loaded or not towing will not
cause damage; however, it is not
recommended and may result in unpleasant
engine and transmission driving
characteristics, heavy or light steering
efforts, and reduced fuel economy.
Integrated Trailer Brake Control System
The vehicle may have an Integrated Trailer
Brake Control (ITBC) system for use with
electric trailer brakes or most electric over
hydraulic trailer brake systems. These
instructions apply to both types of electric
trailer brakes.
This symbol is on the Trailer Brake Control
Panel on vehicles with an ITBC system. The
power output to the trailer brakes is
proportional to the amount of vehicle
braking. This available power output to the
trailer brakes can be adjusted to a wide
range of trailering situations.
The ITBC system is integrated with the
vehicle’s brake, antilock brake, and
StabiliTrak/Electronic Stability Control (ESC)
systems. In trailering conditions that cause
the vehicle’s antilock brake or StabiliTrak/
ESC systems to activate, power sent to the
trailer's brakes will be automatically
adjusted to minimize trailer wheel lock-up.
This does not imply that the trailer has
StabiliTrak/ESC.
If the vehicle’s brake, antilock brake,
or StabiliTrak/ESC systems are not
functioning properly, the ITBC system may
not function fully or at all. Make sure all of
these systems are fully operational to allow
the ITBC system to function properly.
The ITBC system is powered through the
vehicle's electrical system. Turning the
ignition off will also turn off the ITBC
system. The ITBC system is fully functional
only when the ignition is in on.{Warning
Connecting a trailer that has an air brake
system may result in reduced or
complete loss of trailer braking, including
increased stopping distance or trailer
instability which could result in serious
injury, death, or property damage. Only
use the ITBC system with electric or
electric over hydraulic trailer brake
systems.
Trailer Brake Control Panel
1. Manual Trailer Brake Apply Lever
2. Trailer Symbol
3. Trailer Gain Adjustment Buttons

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
304 Driving and Operating
The trailer symbol on the control panel will
light amber when a trailer with electric
brakes is connected.
The ITBC control panel is on the center
stack. SeeInstrument Panel Overview 04.
The control panel allows adjustment to the
amount of output, referred to as Trailer
Gain, available to the trailer brakes and
allows manual application of the trailer
brakes. Use the ITBC control panel and the
DIC trailer brake display page to adjust and
display power output to the trailer brakes.
Trailer Brake DIC Display Page
The ITBC display page indicates:
.Trailer Gain setting
.Output to the trailer brakes
.Trailer connection
.System operational status
To display:
.Scroll through the DIC menu pages
.Press a Trailer Gain (+) or (−) button
.Activate the Manual Trailer Brake Apply
Lever
TRAILER GAIN: Press a Trailer Gain button to
recall the current Trailer Gain setting. Each
press and release of the gain buttons will
then change the Trailer Gain setting. Press the Trailer Gain (+) or (-) to adjust. Press and
hold to continuously adjust the Trailer Gain.
To turn the output to the trailer off, adjust
the Trailer Gain setting to 0.0. This setting
can be adjusted from 0.0 to 10.0 with a
trailer connected or disconnected.
TRAILER OUTPUT: This displays anytime a
trailer with electric brakes is connected.
Output to the trailer brakes is based on the
amount of vehicle braking present and
relative to the Trailer Gain setting. Output is
displayed from 0 to 100% for each gain
setting.
The Trailer Output will indicate
“- - - - - -”on
the Trailer Brake Display Page whenever the
following occur:
.No trailer is connected.
.A trailer without electric brakes is
connected. No DIC message displays.
.A trailer with electric brakes has become
disconnected. A CHECK TRAILER WIRING
message displays on the DIC.
.There is a fault present in the wiring to
the trailer brakes. A CHECK TRAILER
WIRING message displays on the DIC.
.The ITBC system is not working due to a
fault. A SERVICE TRAILER BRAKE SYSTEM
message displays in the DIC.
Manual Trailer Brake Apply Lever
Slide this lever right to apply the trailer’s
electric brakes independent of the vehicle’s
brakes. Use this lever to adjust the Trailer
Gain to achieve proper power output to the
trailer brakes. Under certain circumstances,
this lever can also be used to apply
additional trailer braking. The trailer and
vehicle brake lamps will come on when
either the vehicle brakes or trailer brakes are
applied and properly connected.
Trailer Gain Adjustment Procedure
Trailer Gain should be set for a specific
trailering condition and it must be
readjusted anytime vehicle loading, trailer
loading, or road surface conditions change.
{Warning
Trailer brakes that are over-gained or
under-gained may not stop the vehicle
and the trailer as intended and can result
in a crash. Always follow the instructions
to set the Trailer Gain for the proper
trailer stopping performance.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 305
To adjust Trailer Gain for each towing
condition:1. Drive the vehicle with the trailer attached on a level road surface
representative of the towing condition
and free of traffic at about 32–40 km/h
(20–25 mph) and fully apply the Manual
Trailer Brake Apply Lever.
Adjusting Trailer Gain at speeds lower
than 32–40 km/h (20–25 mph) may
result in an incorrect gain setting.
2. Adjust the Trailer Gain, using the Trailer Gain (+) or (−) adjustment buttons, to
just below the point of trailer wheel
lock-up, indicated by trailer wheel squeal
or tire smoke when a trailer wheel locks.
Trailer wheel lock-up may not occur if
towing a heavily loaded trailer. Adjust
the Trailer Gain to the highest allowable
setting for the towing condition.
3. Readjust Trailer Gain anytime vehicle loading, trailer loading, or road surface
conditions change or if trailer wheel
lock-up is noticed at any time while
towing.Other ITBC-Related DIC Messages
TRAILER CONNECTED: This message will
briefly display when a trailer with electric
brakes is first connected to the vehicle. This
message will automatically turn off in about
10 seconds. This message can be
acknowledged before it automatically
turns off.
CHECK TRAILER WIRING: This message will
display if:
.The ITBC system first determines
connection to a trailer with electric brakes
and then the trailer harness becomes
disconnected from the vehicle.
If the disconnect occurs while the vehicle
is stationary, this message will
automatically turn off in about
30 seconds. This message will also turn
off if it is acknowledged or if the trailer
harness is reconnected.
If the disconnect occurs while the vehicle
is moving, this message will continue
until the ignition is turned off. This
message will also turn off if it is
acknowledged or if the trailer harness is
reconnected.
.There is an electrical fault in the wiring to
the trailer brakes. This message will
continue as long as there is an electrical
fault in the trailer wiring. This message
will also turn off if it is acknowledged.
To determine whether the electrical fault is
on the vehicle side or trailer side of the
trailer wiring harness connection: 1. Disconnect the trailer wiring harness from the vehicle.
2. Turn the ignition off.
3. Wait 10 seconds, then turn the ignition back to RUN.
4. If the CHECK TRAILER WIRING message reappears, the electrical fault is on the
vehicle side.
If the CHECK TRAILER WIRING message only
reappears when connecting the trailer wiring
harness to the vehicle, the electrical fault is
on the trailer side.
SERVICE TRAILER BRAKE SYSTEM: This
message will display when there is a
problem with the ITBC system. If this
message continues over multiple ignition
cycles, have the vehicle serviced.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
306 Driving and Operating
If either the CHECK TRAILER WIRING or
SERVICE TRAILER BRAKE SYSTEM message
displays while driving, the ITBC system may
not be fully functional or may not function
at all. When traffic conditions allow,
carefully pull the vehicle over to the side of
the road and turn the ignition off. Check the
wiring connection to the trailer and turn the
ignition back on. If either of these messages
continues, either the vehicle or trailer needs
service.
A GM dealer may be able to diagnose and
repair problems with the trailer. However,
any diagnosis and repair of the trailer is not
covered under the vehicle warranty. Contact
your trailer dealer for assistance with trailer
repairs and trailer warranty information.
Trailer Sway Control (TSC)
Vehicles with StabiliTrak/Electronic Stability
Control (ESC) have a Trailer Sway Control
(TSC) feature. Trailer sway is unintended
side-to-side motion of a trailer while towing.
If the vehicle is towing a trailer and the TSC
detects that sway is increasing, the vehicle
brakes are selectively applied at each wheel,
to help reduce excessive trailer sway.
If equipped with the Integrated Trailer BrakeControl (ITBC) system, and the trailer has an
electric brake system, StabiliTrak/ESC may
also apply the trailer brakes.
If TSC is enabled, the Traction Control
System (TCS)/StabiliTrak/ESC warning light
will flash on the instrument cluster. Reduce
vehicle speed by gradually removing your
foot from the accelerator. If trailer sway
continues, StabiliTrak/ESC can reduce engine
torque to help slow the vehicle. TSC will not
function if StabiliTrak/ESC is turned off. See
Traction Control/Electronic Stability Control
0
248.
{Warning
Trailer sway can result in a crash and in
serious injury or death, even if the
vehicle is equipped with TSC.
If the trailer begins to sway, reduce
vehicle speed by gradually removing your
foot from the accelerator. Then pull over
to check the trailer and vehicle to help
correct possible causes, including an
improperly or overloaded trailer,
unrestrained cargo, improper trailer hitch
configuration, or improperly inflated or
incorrect vehicle or trailer tires. See
Towing Equipment 0296 for trailer
ratings and hitch setup recommendations.
Aftermarket Electronic Trailer Sway
Control Devices
Some trailers may come equipped with an
electronic device designed to reduce or
control trailer sway. Aftermarket equipment
manufacturers also offer similar devices that
connect to the wiring between the trailer
and the vehicle. These devices may interfere
with the vehicle’s trailer brake or other
systems, including integrated anti-sway
systems, if equipped. Messages related to

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 307
trailer connections or trailer brakes could
appear on the DIC. The effects of these
aftermarket devices may have on vehicle
handling or trailer brake performance is not
known.
{Warning
Use of aftermarket electronic trailer sway
control devices could result in reduced
trailer brake performance, loss of trailer
brakes, or other malfunctions, and result
in a crash. You or others could be
seriously injured or killed. Before using
one of these devices:
.Ask the device or trailer manufacturer
if the device has been thoroughly
tested for compatibility with the
make, model, and year of your vehicle
and any optional equipment installed
on your vehicle.
.Before driving, check the trailer brakes
are working properly, if equipped.
Drive the vehicle with the trailer
attached on a level road surface that
is free of traffic at about 32-40 km/h
(20-25 mph) and fully apply the(Continued)
Warning (Continued)
manual trailer brake apply lever. Also,
check the trailer brake lamps and
other lamps are functioning correctly.
.If the trailer brakes are not operating
properly at any time, or if a DIC
message indicates problems with the
trailer connections or trailer brakes,
carefully pull the vehicle over to the
side of the road when traffic
conditions allow.
Trailer Tires
Special Trailer (ST) tires differ from vehicle
tires. Trailer tires are designed with stiff
sidewalls to help prevent sway and to
support heavy loads. These features can
make it difficult to determine if the trailer
tire pressures are low only based on a visual
inspection.
Always check all trailer tire pressures before
each trip when the tires are cool. Low trailer
tire pressure is a leading cause of trailer tire
blow-outs. If the vehicle is equipped with a trailer tire
pressure monitoring system, see the trailer
tire pressure monitoring system description
and the trailering app.
Trailer tires deteriorate over time. The trailer
tire sidewall will show the week and year
the tire was manufactured. Many trailer tire
manufacturers recommend replacing tires
more than six years old.
Overloading is another leading cause of
trailer tire blow-outs. Never load your trailer
with more weight than the tires are
designed to support. The load rating is
located on the trailer tire sidewall.
Always know the maximum speed rating for
the trailer tires before driving. This may be
significantly lower than the vehicle tire
speed rating. The speed rating may be on
the trailer tire sidewall. If the speed rating is
not shown, the default trailer tire speed
rating is 105 km/h (65 mph).
Trailering App
Trailer Lights App
If equipped, the Trailer Lights App is on the
Home Page of the infotainment display.