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GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
262 Driving and Operating
driver seat belt is unbuckled, the ACC
automatically applies the Electric Parking
Brake (EPB) to hold the vehicle. The EPB
status light will turn on. SeeElectric Parking
Brake 0247.
A DIC warning message may display
indicating to shift to P (Park) before exiting
the vehicle. See Vehicle Messages 0130.
{Warning
If ACC has stopped the vehicle, and if ACC
is disengaged, turned off, or canceled, the
vehicle will no longer be held at a stop.
The vehicle can move. When ACC is
holding the vehicle at a stop, always be
prepared to manually apply the brakes.
{Warning
Leaving the vehicle without placing it in
P (Park) can be dangerous. Do not leave
the vehicle while it is being held at a
stop by ACC. Always place the vehicle in
P (Park) and turn off the ignition before
leaving the vehicle. ACC Override
If using the accelerator pedal while ACC is
active, the ACC indicator turns blue on the
instrument cluster and in the HUD,
if equipped, to indicate that automatic
braking will not occur. ACC will resume
operation when the accelerator pedal is not
being pressed.
{Warning
The ACC will not automatically apply the
brakes if your foot is resting on the
accelerator pedal. You could crash into a
vehicle ahead of you.
Curves in the Road
{Warning
On curves, ACC may not detect a vehicle
ahead in your lane. You could be startled
if the vehicle accelerates up to the set
speed, especially when following a vehicle
exiting or entering exit ramps. You could
lose control of the vehicle or crash. Do
not use ACC while driving on an entrance
or exit ramp. Always be ready to use the
brakes if necessary.
{Warning
On curves, ACC may respond to a vehicle
in another lane, or may not have time to
react to a vehicle in your lane. You could
crash into a vehicle ahead of you, or lose
control of your vehicle. Give extra
attention in curves and be ready to use
the brakes if necessary. Select an
appropriate speed while driving in curves.
ACC may operate differently in a sharp
curve. It may reduce the vehicle speed if the
curve is too sharp. ACC automatically slows
the vehicle down while navigating the curve
and may increase speed out of the curve,
but will not exceed the set speed.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
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Driving and Operating 281
When the vehicle is started, both outside
mirror LCA displays will briefly come on to
indicate the system is operating. When the
vehicle is in a forward gear, the left or right
side mirror display will light up if a moving
vehicle is detected in the next lane over in
that blind zone or rapidly approaching that
zone. If the turn signal is activated in the
same direction as a detected vehicle, this
display will flash as an extra warning not to
change lanes.
LCA can be disabled through vehicle
personalization. When you disable LCA, SBZA
is also disabled. SeeVehicle Personalization
0 131. If LCA is disabled by the driver, the
LCA mirror displays will not light up.
When the System Does Not Seem to
Work Properly
The LCA system requires some driving for
the system to calibrate to maximum
performance. This calibration may occur
more quickly if the vehicle is driving on a
straight highway road with traffic and
roadside objects (e.g., guardrails, barriers).
LCA displays may not come on when
passing a vehicle quickly, for a stopped
vehicle, or when towing a trailer. The LCA
detection zones that extend back from the side of the vehicle do not move further back
when a trailer is towed. Use caution while
changing lanes when towing a trailer. LCA
may alert to objects attached to the vehicle,
such as a trailer, bicycle, or object extending
out to either side of the vehicle. Attached
objects may also interfere with the
detection of vehicles. This is normal system
operation; the vehicle does not need service.
LCA may not always alert the driver to
vehicles in the next lane over, especially in
wet conditions or when driving on sharp
curves. The system does not need to be
serviced. The system may light up due to
guardrails, signs, trees, shrubs, and other
non-moving objects. This is normal system
operation; the vehicle does not need service.
LCA may not operate when the LCA sensors
in the left or right corners of the rear
bumper are covered with mud, dirt, snow,
ice, or slush, or in heavy rainstorms. For
cleaning instructions, see "Washing the
Vehicle" under
Exterior Care0398. If the
DIC still displays the system unavailable
message after cleaning both sides of the
vehicle toward the rear corners of the
vehicle, see your dealer. If the LCA displays do not light up when
moving vehicles are in the side blind zone or
are rapidly approaching this zone and the
system is clean, the system may need
service. Take the vehicle to your dealer.
Radio Frequency Information
See
Radio Frequency Statement 0436.
Lane Keep Assist (LKA)
If equipped, LKA may help avoid crashes due
to unintentional lane departures. This
system uses a camera to detect lane
markings between 60 km/h (37 mph) and
180 km/h (112 mph). It may assist by gently
turning the steering wheel if the vehicle
approaches a detected lane marking. It may
also provide a Lane Departure Warning
(LDW) alert if the vehicle crosses a detected
lane marking. LKA can be overridden by
turning the steering wheel. This system is
not intended to keep the vehicle centered in
the lane. LKA will not assist and alert if the
turn signal is active in the direction of lane
departure, or if it detects that you are
accelerating, braking or actively steering.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
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286 Driving and Operating
Warning (Continued)
.Keep children away from the fuel
pump and never let children
pump fuel.
.Before touching the fill nozzle, touch a
metallic object to discharge static
electricity from your body.
.Fuel can spray out if the fill nozzle is
inserted too quickly. This spray can
happen if the tank is nearly full, and is
more likely in hot weather. Insert the
fill nozzle slowly and wait for any hiss
noise to stop before beginning to
flow fuel.
The capless refueling system does not have
a fuel cap. Fully insert and latch the fill
nozzle, begin fueling.
{Warning
Overfilling the fuel tank by more than
three clicks of a standard fill nozzle may
cause:
.Vehicle performance issues, including
engine stalling and damage to the fuel
system.
.Fuel spills.
.Under certain conditions, fuel fires.
Be careful not to spill fuel. Wait five seconds
after you have finished pumping before
removing the fill nozzle. Clean fuel from
painted surfaces as soon as possible. See
Exterior Care 0398. Push the fuel door
closed.
{Warning
If a fire starts while you are refueling, do
not remove the fill nozzle. Shut off the
flow of fuel by shutting off the pump or
by notifying the station attendant. Leave
the area immediately. Filling the Tank with a Portable Fuel
Container
If the vehicle runs out of fuel and must be
filled from a portable fuel container:
1. Locate the capless funnel adapter.
2. Insert and latch the funnel into the
capless fuel system.
{Warning
Attempting to refuel from a portable fuel
container without using the funnel
adapter may cause fuel spillage and
damage the capless fuel system. This
could cause a fire. You or others could be
badly burned and the vehicle could be
damaged.
3. Remove and clean the funnel adapter and return it to the storage location.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
288 Driving and Operating
{Warning
If a fire starts while you are refueling, do
not remove the fill nozzle. Shut off the
flow of fuel by shutting off the pump or
by notifying the station attendant. Leave
the area immediately.
Caution
If a new fuel cap is needed, get the right
type of cap from your dealer. The wrong
type of fuel cap may not fit properly,
may turn on the malfunction indicator
lamp, and could damage the fuel system
and emissions system. SeeMalfunction
Indicator Lamp (Check Engine Light) 0115.
Filling a Portable Fuel Container
{Warning
Never fill a portable fuel container while
it is in the vehicle. Static electricity
discharge from the container can ignite
the fuel vapor. You or others could be
badly burned and the vehicle could be
damaged. To help avoid injury to you
and others:
.Dispense fuel only into approved
containers.
.Do not fill a container while it is
inside a vehicle, in a vehicle's trunk, in
a pickup bed, or on any surface other
than the ground.
.Bring the fill nozzle in contact with
the inside of the fill opening before
operating the nozzle. Maintain contact
until filling is complete.
.Keep sparks, flames, and smoking
materials away from fuel.
.Avoid using electronic devices while
pumping fuel.
Trailer Towing
General Towing Information
Only use towing equipment that has been
designed for the vehicle. Contact your dealer
or trailering dealer for assistance with
preparing the vehicle to tow a trailer. Read
the entire section before towing a trailer.
To tow a disabled vehicle, see Towing the
Vehicle 0394. To tow the vehicle behind
another vehicle such as a motor home, see
Recreational Vehicle Towing 0395.
Driving Characteristics and
Towing Tips
{Warning
You can lose control when towing a
trailer if the correct equipment is not
used or the vehicle is not driven properly.
For example, if the trailer is too heavy or
the trailer brakes are inadequate for the
load, the vehicle may not stop as
expected. You and others could be
seriously injured. The vehicle may also be
damaged, and the repairs would not be
covered by the vehicle warranty. Pull a
(Continued)

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 291
Driving on Grades
Reduce speed and shift to a lower gear
before starting down a long or steep
downhill grade. If the transmission is not
shifted down, the brakes may overheat and
result in reduced braking efficiency.
The vehicle can tow in D (Drive). Shift the
transmission to a lower gear if the
transmission shifts too often under heavy
loads and/or hilly conditions.
When towing at higher altitudes, engine
coolant will boil at a lower temperature
than at lower altitudes. If the engine is
turned off immediately after towing at high
altitude on steep uphill grades, the vehicle
could show signs similar to engine
overheating. To avoid this, let the engine
run, preferably on level ground, with the
transmission in P (Park) for a few minutes
before turning the engine off. If the
overheat warning comes on, seeEngine
Overheating 0338.
Viewing Systems
If equipped, the viewing systems on the
vehicle can improve visibility while hitching,
backing, and driving with a trailer. See
Driver Assistance Systems 0265.
Parking on Hills
{Warning
To prevent serious injury or death,
always park your vehicle and trailer on a
level surface when possible.
When parking your vehicle and your trailer
on a hill: 1. Press the brake pedal, but do not shift into P (Park) yet. Turn the wheels into
the curb if facing downhill or into traffic
if facing uphill.
2. Have someone place chocks under the trailer wheels.
3. Gradually release the brake pedal to allow the chocks to absorb the load of
the trailer.
4. Reapply the brake pedal. Then apply the parking brake and shift into P (Park).
5. Release the brake pedal.
Leaving After Parking on a Hill
1. Apply and hold the brake pedal.
.Start the engine.
.Shift into a gear.
.Release the parking brake. 2. Let up on the brake pedal.
3. Drive slowly until the trailer is clear of
the chocks.
4. Stop and have someone pick up and store the chocks.
Launching and Retrieving a Boat
Backing the Trailer into the Water
{Warning
.Have all passengers get out of the
vehicle before backing onto the sloped
part of the ramp. Lower the driver and
passenger side windows before
backing onto the ramp. This will
provide a means of escape in the
unlikely event the vehicle slides into
the water.
.If the boat launch surface is slippery,
have the driver remain in the vehicle
with the brake pedal applied while the
boat is being launched. The boat
launch can be especially slippery at
low tide when part of the ramp was
previously submerged at high tide. Do
not back onto the ramp to launch the
boat if you are not sure the vehicle
can maintain traction.
(Continued)

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
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./
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308 Driving and Operating
Touch Start to cycle the trailer lamps on and
off to determine if they are working. The
test follows this sequence:1. The running lights turn on first and remain on throughout the sequence.
2. The brake lights turn on for about two seconds.
3. The left turn signal light flashes three times.
4. The right turn signal light flashes three times.
5. The reverse lights turn on for about two seconds.
6. Steps 2–5 repeat for approximately one minute and 45 seconds, or until the
test deactivates.
Touch Stop to stop the test. The test will
automatically end after one minute and
45 seconds.
The sequence also deactivates when any of
the following occur:
.The ignition is turned off.
.The transmission is shifted out of P (Park).
.The brake pedal is pressed.
.The turn signal is activated.
.The hazard warning lights are activated.
Trailering App
If equipped, the Trailering App is on the
Home Page of the infotainment display.
If equipped this feature allows profiles for
connected trailers to be created to view
status, to store and track trailer usage
information, and to set up towing assistance
features.
The Trailering App Preview will appear when
the Trailering App is opened for the first
time from the Home Page. Touch GET
STARTED in the Trailering App to go into
the app.
When a trailer is electrically connected and
a trailer profile has not been created, there
will be an option to create a profile, use a
guest profile, or select Accessory/No trailer.
After the pop-up is displayed three times,
Don’t Remind Me will display and touching
that will turn off the trailer detection
pop-up. To turn the Trailer Detection Alert
on, select ON in the Settings tab.
When a trailer is electrically connected and
after a Trailer Profile has been created, the
trailer detection pop-up will appear with a
list of all of the custom Trailer Profiles made
on the vehicle. To load an existing Trailer
Profile, select one of the Trailer Profiles listed, or load the Guest Trailer Profile by
selecting GUEST TRAILER. Touching
Accessory/No trailer will select Accessory/No
trailer as the active Trailer Profile and will
dismiss the pop- up. Shifting the vehicle
from P (Park) will select Guest Trailer as the
active Trailer Profile and will dismiss the
pop-up.
Create a Trailer Profile
1. Touch Create Profile on the trailer detection pop-up or touch + Add Trailer
Profile in the Trailering App.
2. Create a name for the trailer.
3. Select the trailer type.
4. Select Save Profile.
A pop-up will indicate the setup is complete.
Touch DONE to complete the process or
touch TRAILER FEATURE SETUP to set up the
Tow/Haul Mode reminder, Trailer Tire
Pressure Monitoring System, if equipped,
maintenance reminders, or towing
assistance, if equipped.
Import a Trailer Profile
A trailer profile saved to an OnStar account
can be imported to the vehicle. 1. Touch + Add Trailer Profile in the Trailering App

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Driving and Operating 309
2. Touch Import Profile on the pop-up.
3. Select a trailer profile from the list.
4. Touch IMPORT.
A pop-up will indicate the import was
successful. Touch OK to return to the trailer
list and select the trailer profile. The Tow/
Haul Mode reminder, Brake Gain Setting and
Trailer Tire Pressure sensor learning,
if equipped, do not import.
Trailer Feature Setup
Tow/Haul Mode Reminder
To turn the Tow/Haul Mode Reminder
setting on, touch Yes. To turn it off,
touch No.
Trailer Tire Pressure Setup
If the Trailer Tire Pressure Monitoring
System (TTPMS) is detected, touch the Tire
Pressure Monitoring icon to set up tire
pressure monitoring. Touch Yes to set up
the sensors or touch No to return to the
previous screen.
The trailer tire pressure sensors can transmit
up to 7 m (23 feet) from the hitch receiver of
the vehicle. A trailer must be electrically connected to
the vehicle before starting the
sensor-to-vehicle learn process.
After selecting Start from the Learn Sensors
screen, use the Tool Method or the Manual
Method (described below) to learn each tire
sensor, during which the current tire number
will be highlighted.
Each sensor has a minimum of two minutes
to learn, shown by a timer. After a sensor is
learned, a checkmark appears next to the
tire, the vehicle horn will sound, the
vehicle’s brake lamps will flash, and all
working trailer lamps will flash. It then
moves to the next sensor.
To cancel the process touch Stop.
The recommended tire pressure must be
entered for the trailer tires. This allows the
vehicle to alert when the tire pressure is
high or low.
TTPMS must learn the location of the
installed tire sensors to show correct air
pressure and temperature for each tire. To
set up, use one of the following options or
see a tire or trailer dealer for service. The
learning process must be repeated when thetrailer tires are rotated or replaced. See
“Editing a Trailer Profile”
later in this section
for tire pressure sensor relearn information.
Tool Method: A TTPMS activation tool can
be purchased separately to learn the sensor
locations.
Manual Method: Without the tool, the air
pressure can be increased or decreased in
each tire for 10 seconds. Do not exceed the
maximum inflation pressure found on the
tire sidewalls. Make sure to re-adjust tire
pressure to the recommended level when
the process is complete.
Sensor Learning Steps
To complete the sensor-to-vehicle learn
process:
1. Touch Start on the Learn Sensors screen. The horn chirps twice and the Learning
Active screen appears on the
infotainment display.
2. Start with the driver side front trailer tire.
3. Activate the tool near the valve stem or adjust the air pressure of this tire until
the horn chirps and all working vehicle
and trailer lights flash.

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Driving and Operating 311
Trailer Side Blind Zone Alert Setup (if
equipped)
Trailer dimensions must be in range to
enable this feature.
.Trailer Length: 300 cm (118.1 in)–
1200 cm (472.4 in). Measure from center
of coupler to furthest rear point on the
trailer.
If trailer dimensions are out of range, this
feature will be unavailable.
Status View
The Status view shows:
.Vehicle
.Connections
.Tires
.Maintenance
.Cameras
Upon entry, the most recent items will be
shown. Select MORE to view all options.
Vehicle
1. Transmission Fluid Temperature
2. Average Fuel Economy with Trailer Profile
Transmission Temperature
View the temperature of the transmission
fluid by looking at the graphic. The graphic
will indicate a dangerous level if the
temperature is at 130 °C–150 °C
(270 °F–300 °F).
Average Fuel Economy
Touch to view the average fuel economy of
the vehicle while the Trailer Profile is active.
Connections
1. Light Test Start Button
2. Trailer Electrical Diagnostics
Connections: OK
If a trailer connection is detected, the view
will display OK.
Trailer Connections Status
When a trailer is connected, the Trailering
App System detects the trailer connection
using the Park and Stop/Turn Signal lighting
circuits and alerts the driver by requesting a
trailer profile setup through the Trailering
App System on the infotainment screen. The
Trailer Detection Alert setting must be
enabled for the alert to display when a