towing GMC SIERRA 2021 Owner's Guide

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
292 Driving and Operating
Warning (Continued)
.Do not move the vehicle if someone is
in the path of the trailer. Some parts
of the trailer might be underwater and
not visible to people who are assisting
in launching the boat.
Disconnect the wiring to the trailer before
backing the trailer into the water to prevent
damage to the electrical circuits on the
trailer. Reconnect the wiring to the trailer
after removing the trailer from the water.
If the trailer has electric brakes that can
function when the trailer is submerged, it
might help to leave the electrical trailer
connector attached to maintain trailer brake
functionality while on the boat ramp.
To back the trailer into the water: 1. If equipped, place the vehicle in four-wheel-drive high.
2. Slowly back down the boat ramp until the boat is floating, but no further than
necessary.
3. Press and hold the brake pedal, but do not shift into P (Park) yet.
4. Have someone place chocks under the front wheels of the vehicle. 5. Gradually release the brake pedal to
allow the chocks to absorb the load of
the trailer.
6. Reapply the brake pedal. Then apply the parking brake and shift into P (Park).
7. Release the brake pedal.
Pulling the Trailer from the Water
To pull the trailer out of the water: 1. Press and hold the brake pedal.
2. Start the engine and shift into gear.
3. Release the parking brake.
4. Let up on the brake pedal.
5. Drive slowly until the tires are clear of the chocks.
6. Stop and have someone pick up and store the chocks.
7. Slowly pull the trailer from the water.
8. Once the vehicle and trailer have been driven from the sloped part of the boat
ramp, the vehicle can be shifted from
four-wheel-drive high. Shift into the drive
mode that is appropriate for the road
conditions.
Caution
If the vehicle tires begin to spin and the
vehicle begins to slide toward the water,
remove your foot from the accelerator
pedal and apply the brake pedal. Seek
help to have the vehicle towed up
the ramp.
Maintenance when Trailer Towing
The vehicle needs service more often when
used to tow trailers. See Maintenance
Schedule 0409. It is especially important to
check the engine oil, axle lubricant, belts,
cooling system, and brake system before
and during each trip.
Check periodically to see that all nuts and
bolts on the trailer hitch are tight.
Engine Cooling When Trailer Towing
The cooling system may temporarily
overheat during severe operating conditions.
See Engine Overheating 0338.

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
296 Driving and Operating
After loading the trailer, separately weigh
the trailer and then the trailer tongue and
calculate the trailer load balance percentage
to see if the weights and distribution are
appropriate for your vehicle. If the trailer
weight is too high, it may be possible to
transfer some of the cargo into your vehicle.
If the trailer tongue weight is too high or
too low, it may be possible to rearrange
some of the cargo inside of the trailer.
Do not exceed the maximum allowable
tongue weight for your vehicle. Use the
shortest hitch extension available to position
the hitch ball closer to your vehicle. This will
help reduce the effect of the trailer tongue
weight on the trailer hitch and the rear axle.
If a cargo carrier is used in the trailer hitch
receiver, choose a carrier that positions the
load as close to the vehicle as possible.
Make sure the total weight, including the
carrier, is no more than half of the
maximum allowable tongue weight for the
vehicle or 227 kg (500 lb), whichever is less.Rear Gross Axle Weight Rating
(GAWR-RR)
The GAWR-RR is the total weight that can be
supported by the rear axle of the vehicle. Do
not exceed the GAWR-RR for the vehicle,
with the tow vehicle and trailer fully loaded
for the trip including the weight of the
trailer tongue. If using a weight-distributing
hitch, do not exceed the GAWR-RR before
applying the weight distribution spring bars.
The GAWR-RR for the vehicle is on the
Trailering Information Label.
Ask your dealer for trailering information or
assistance.
Towing Equipment
Hitches
{Warning
In order to avoid serious injury or
property damage, always follow the hitch
manufacturer's instructions when securing
your draw bar/coupling device to the
vehicle's hitch receiver.
Ensure that the draw bar/coupling device
is secured with a locking retainer pin or
other means such that rotation of the pin
or locking mechanism will not cause the
pin to back out or loosen during use.
Failure to correctly secure the draw bar/
coupling device to the receiver can result
in separation of the hitch/receiver while
towing.
Conventional Hitch
A conventional hitch is bolted to the frame
or cross member of the tow vehicle, and is
generally rated Class 2, 3, or 4.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 297
Gooseneck Hitch
A gooseneck hitch is designed to be coupled
to a special hitch leveraging a hitch ball, and
is mounted over the rear axle in the
truck bed.
Fifth-Wheel Hitch
A fifth-wheel hitch is mounted over the rear
axle in the truck bed, and leverages a
hinged plate—the same type of hitch
leveraged by semi trucks. Generally,
fifth-wheel hitches accommodate large
trailers with as many as one, two, or three
axles.
Always use the correct hitch equipment for
your vehicle. Crosswinds, large trucks going
by, and rough roads can affect the trailer
and the hitch.
Proper hitch equipment for your vehicle
helps maintain control of the vehicle-trailer
combination. Many trailers can be towed
using a weight-carrying hitch which has a
coupler latched to the hitch ball, or a tow
eye latched to a pintle hook. Other trailers
may require a weight-distributing hitch that
uses spring bars to distribute the trailer tongue weight between your vehicle and
trailer axles. Fifth-wheel and gooseneck
hitches may also be used. See
“Maximum
Trailer Tongue Weight” underTrailer Towing
0 293 for weight limits with various hitch
types.
Avoid sharp turns when using a step-bumper
hitch to prevent damage. Make wider turns
to prevent contact between your trailer and
your bumper.
Consider using mechanical sway controls
with any trailer. Ask a trailering professional
about sway controls or refer to the trailer
manufacturer's recommendations and
instructions.
Weight-Distributing Hitch and
Adjustment
A weight-distributing hitch may be useful
with some trailers. Use the following
guidelines to determine if a
weight-distributing hitch should be used.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
298 Driving and Operating
Vehicle SeriesTrailer Weight Weight-Distributing Hitch Usage Hitch Distribution
1500 Up to 3 175 kg (7,000 lb) Not Required50%
1500 Over 3 175 kg (7,000 lb) Required50%
1. Front of Vehicle
2. H1/H2 Body to Ground Distance
Towing with Model 1500 Series Trucks
1. Position the truck so that the trailer is ready to connect (keep the trailer
detached).
2. Measure the height of the top of the front wheel opening at the fender to the
ground (H1).
3. Attach the vehicle to the trailer, do not attach weight distribution bars at
this time.
4. Measure the height of the top of the front wheel opening on the fender to
the ground (H2). 5. Install and adjust the tension in the
weight-distributing bars per the
manufacturers’ recommendations so that
the height of the front fender is
approximately H2−[(H2−H1)/2] (halfway
between the two measured ride heights).
6. Visually inspect the trailer and weight-distributing hitch to ensure that
the manufacturers’ recommendations
have been met.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 299
MeasurementHeight Example 1500 (mm)
H1 1 000
H2 1 050
H2−H1 50
(H2−H1)/2 25
H2−[(H2−H1)/2] 1 025
Tires
.Do not tow a trailer while using a
compact spare tire on the vehicle.
.Tires must be properly inflated to support
loads while towing a trailer. SeeTires
0 360 for instructions on proper tire
inflation.
Fifth-Wheel and Gooseneck Trailering
Fifth-wheel and gooseneck trailers can be
used with many pickup models. These
trailers place a larger percentage of the
weight (kingpin weight) on the tow vehicle
than conventional trailers. Make sure this
weight does not cause the vehicle to exceed
GAWR or GVWR. Fifth-wheel or gooseneck
kingpin weight should be 15–25% of the
trailer weight up to the maximum amount specified in the trailering chart for the
vehicle. See
“Trailer Weight" under Trailer
Towing 0293.
The hitch should be in the pickup bed so
that its centerline is over or slightly in front
of the rear axle. Take care that it is not so
far forward that it will contact the back of
the cab in sharp turns. This is especially
important for short box pickups. Trailer pin
box extensions and sliding fifth-wheel hitch
assemblies may be used. There should be at
least 15 cm (6 in) of clearance between the
top of the pickup box and the bottom of the
trailer shelf that extends over the box.
Make sure the hitch is attached to the tow
vehicle frame rails. Do not use the pickup
box for support.
Safety Chains
Always attach safety chains between the
vehicle and the trailer. Instructions about
safety chains may be provided by the hitch
manufacturer or by the trailer manufacturer.
If the trailer being towed weighs up to
2 271 kg (5,000 lb) with a factory-installed
step bumper, safety chains may be attached
to the attaching points on the bumper;
otherwise, safety chains should be attached
to holes on the trailer hitch.
Cross the safety chains under the tongue of
the trailer to help prevent the tongue from
contacting the road if it becomes separated
from the hitch. Always leave enough slack in
the safety chains to allow the combination
to turn. Never allow safety chains to drag
on the ground.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
302 Driving and Operating
Camper/Fifth-Wheel Trailer Wiring Package
For vehicles without the fifth wheel/
gooseneck trailer package, the seven-wire
camper harness is under the rear bumper,
attached to the frame near the rear
crossmember. A connector must be added to
the wiring harness that connects to the
camper.
The harness contains the following camper/
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 with the heavy-duty trailering
option, see “Heavy-Duty Trailer Wiring
Harness Package” earlier in this section.
When the camper-wiring harness is ordered
without the heavy-duty trailering package, a
seven-wire harness with a seven-pin
connector is at the rear of the vehicle and is
tied to the vehicle's frame.
Trailer Lamps
Always check that all trailer lamps are
working at the beginning of each trip, and
periodically on longer trips.
If equipped, the Trailering App will monitor
the RH turn/brake lamp circuit, LH turn/
brake lamp circuit, running lamp circuit, and
reverse lamp circuits on the trailer. DIC
messages and Trailering App alerts may be
displayed if lighting circuit issues are
detected on the trailer. Pressing START LIGHT TEST in the Trailering
App automatically activates the trailer
lamps. The Trailering App is not a substitute
for manually inspecting your trailer lamps.
See
Trailering App 0307.
Turn Signals When Towing a Trailer
When properly connected, the trailer turn
signals will illuminate to indicate the vehicle
is turning, changing lanes, or stopping.
When towing a trailer, the arrows on the
instrument cluster will illuminate even if the
trailer is not properly connected or the bulbs
are burned out.
Tow/Haul Mode
For instructions on how to enter Tow/Haul
Mode, see Driver Mode Control 0251.
Tow/Haul assists when pulling a heavy
trailer or a large or heavy load. See Tow/
Haul Mode 0242.
Tow/Haul Mode is designed to be most
effective when the vehicle and trailer
combined weight is at least 75% of the
vehicle's Gross Combined Weight Rating
(GCWR). See “Trailer Weight” underTrailer
Towing 0293.

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
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