2021 GMC SIERRA towing speed

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
116 Instruments and Controls
Caution
If the vehicle is driven continually with
this light on, the emission control system
may not work as well, the fuel economy
may be lower, and the vehicle may not
run smoothly. This could lead to costly
repairs that might not be covered by the
vehicle warranty.
Caution
Modifications to the engine, transmission,
exhaust, intake, or fuel system, or the
use of replacement tires that do not
meet the original tire specifications, can
cause this light to come on. This could
lead to costly repairs not covered by the
vehicle warranty. This could also affect
the vehicle’s ability to pass an Emissions
Inspection/Maintenance test. See
Accessories and Modifications0323.
If the light is flashing : A malfunction has
been detected that could damage the
emission control system and increase vehicle
emissions. Diagnosis and service may be
required. To help prevent damage, reduce vehicle
speed and avoid hard accelerations and
uphill grades. If towing a trailer, reduce the
amount of cargo being hauled as soon as
possible.
If the light continues to flash, find a safe
place to park. Turn the vehicle off and wait
at least 10 seconds before restarting the
engine. If the light is still flashing, follow
the previous guidelines and see your dealer
for service as soon as possible.
If the light is on steady :
A malfunction has
been detected. Diagnosis and service may be
required.
Check the following:
.If fuel has been added to the vehicle
using the capless funnel adapter, make
sure that it has been removed. See
“Filling the Tank with a Portable
Gas Can” underFilling the Tank (Pickup
Model) 0285 or
Filling the Tank (Chassis Cab Model) 0287. The diagnostic system can
detect if the adapter has been left
installed in the vehicle, allowing fuel to
evaporate into the atmosphere. A few
driving trips with the adapter removed
may turn off the light.
.Poor fuel quality can cause inefficient
engine operation and poor driveability,
which may go away once the engine is
warmed up. If this occurs, change the fuel
brand. It may require at least one full
tank of the proper fuel to turn the light
off. See Recommended Fuel (Except 6.2L
V8 Engine) 0283 or
Recommended Fuel (6.2L V8 Engine)
0 284.
If the light remains on, see your dealer.
Emissions Inspection and Maintenance
Programs
If the vehicle requires an Emissions
Inspection/Maintenance test, the test
equipment will likely connect to the
vehicle's Data Link Connector (DLC).
The DLC is under the instrument panel to
the left of the steering wheel. Connecting
devices that are not used to perform an
Emissions Inspection/Maintenance test or to

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Instruments and Controls 117
service the vehicle may affect vehicle
operation. SeeAdd-On Electrical Equipment
0 318. See your dealer if assistance is
needed.
The vehicle may not pass inspection if:
.The light is on when the engine is
running.
.The light does not come on when the
ignition is on while the engine is off.
.Critical emission control systems have not
been completely diagnosed. If this
happens, the vehicle would not be ready
for inspection and might require
several days of routine driving before the
system is ready for inspection. This can
happen if the 12-volt battery has recently
been replaced or run down, or if the
vehicle has been recently serviced.
See your dealer if the vehicle will not pass
or cannot be made ready for the test.
Brake System Warning Light
MetricEnglish
This light should come on briefly when the
vehicle is turned on. If it does not come on
then, have it fixed so it will be ready to
warn you if there is a problem.
If the light comes on and stays on at start
up, there is a brake problem. Have the brake
system inspected right away.
If the light comes on while driving, pull off
the road and stop carefully. If equipped with
electric brake boost, vehicle speed may be
limited when the brake system warning
light comes on. The brake pedal might be
harder to push, or the brake pedal may go
closer to the floor. It could take longer to
stop. If the light is still on, have the vehicle
towed for service. See Towing the Vehicle
0 394.
{Warning
The brake system might not be working
properly if the brake system warning
light is on. Driving with the brake system
warning light on can lead to a crash.
If the light is still on after the vehicle has
been pulled off the road and carefully
stopped, have the vehicle towed for
service.
Electric Parking Brake Light
MetricEnglish
This light comes on when the parking brake
is applied. If the light continues flashing
after the parking brake is released, or while
driving, there is a problem with the Electric
Parking Brake system. A message may also
display in the Driver Information
Center (DIC).
If the light does not come on, or remains
flashing, see your dealer.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
212 Driving and Operating
Filling a Portable Fuel Container . . . . . . . 288
Trailer Towing
General Towing Information . . . . . . . . . . 288
Driving Characteristics andTowing Tips . . . . . . . . . . . . . . . . . . . . . . . . . 288
Trailer Towing . . . . . . . . . . . . . . . . . . . . . . . . . 293
Towing Equipment . . . . . . . . . . . . . . . . . . . . 296
Trailer Sway Control (TSC) . . . . . . . . . . . . 306
Trailering App . . . . . . . . . . . . . . . . . . . . . . . . . 307
Conversions and Add-Ons
Add-On Electrical Equipment . . . . . . . . . . . 318
Adding a Snow Plow or Similar Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . 318
Pickup Conversion to Chassis Cab . . . . . 320
Driving Information
Driving for Better Fuel Economy
Driving habits can affect fuel mileage. Here
are some driving tips to get the best fuel
economy possible:
.Set the climate controls to the desired
temperature after the engine is started,
or turn them off when not required.
.Avoid fast starts and accelerate smoothly.
.Brake gradually and avoid abrupt stops.
.Avoid idling the engine for long periods
of time.
.When road and weather conditions are
appropriate, use cruise control.
.Always follow posted speed limits or
drive more slowly when conditions
require.
.Keep vehicle tires properly inflated.
.Combine several trips into a single trip.
.Replace the vehicle's tires with the same
TPC Spec number molded into the tire's
sidewall near the size.
.Follow recommended scheduled
maintenance.
Distracted Driving
Distraction comes in many forms and can
take your focus from the task of driving.
Exercise good judgment and do not let other
activities divert your attention away from
the road. Many local governments have
enacted laws regarding driver distraction.
Become familiar with the local laws in
your area.
To avoid distracted driving, keep your eyes
on the road, keep your hands on the
steering wheel, and focus your attention on
driving.
.Do not use a phone in demanding driving
situations. Use a hands-free method to
place or receive necessary phone calls.
.Watch the road. Do not read, take notes,
or look up information on phones or
other electronic devices.
.Designate a front seat passenger to
handle potential distractions.
.Become familiar with vehicle features
before driving, such as programming
favorite radio stations and adjusting
climate control and seat settings. Program
all trip information into any navigation
device prior to driving.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
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Driving and Operating 221
Warning (Continued)
.Fully open the air outlets on or under
the instrument panel.
.Adjust the climate control system to
circulate the air inside the vehicle and
set the fan speed to the highest
setting. See“Climate Control Systems.”
For more information about CO, see
Engine Exhaust 0238.
To save fuel, run the engine for short
periods to warm the vehicle and then shut
the engine off and partially close the
window. Moving about to keep warm also
helps.
If it takes time for help to arrive, when
running the engine, push the accelerator
pedal slightly so the engine runs faster than
the idle speed. This keeps the battery
charged to restart the vehicle and to signal
for help with the headlamps. Do this as
little as possible, to save fuel.
If the Vehicle Is Stuck
Slowly and cautiously spin the wheels to
free the vehicle when stuck in sand, mud,
ice, or snow. See “Rocking the Vehicle to Get
It Out” later in this section. The Traction Control/Electronic Stability
Control can often help to free a stuck
vehicle. See
Traction Control/Electronic
Stability Control 0248. If TC/ESC cannot free
the vehicle, see “Rocking the Vehicle to Get
it Out” following.
{Warning
If the vehicle's tires spin at high speed,
they can explode, and you or others
could be injured. The vehicle can
overheat, causing an engine compartment
fire or other damage. Spin the wheels as
little as possible and avoid going above
56 km/h (35 mph).
For information about using tire chains on
the vehicle, see Tire Chains0379.
Rocking the Vehicle to Get It Out
Caution
Do not hold the steering wheel at full
rotation for more than 15 seconds and/or
at an elevated RPM. Damage may occur
to the power steering system and there
may be loss of power steering assist. Turn the steering wheel left and right to
clear the area around the front wheels. Then
make sure the wheels are pointed straight
ahead. For four-wheel-drive vehicles, shift
into Four-Wheel Drive High. Turn the TCS
off. Shift back and forth between R (Reverse)
and a forward gear, spinning the wheels as
little as possible. To prevent transmission
wear, wait until the wheels stop spinning
before shifting gears. Slowly spinning the
wheels in the forward and reverse directions
causes a rocking motion that could free the
vehicle. If that does not get the vehicle out
after a few tries, it might need to be towed
out. See
Towing the Vehicle 0394. Recovery
hooks can be used, if the vehicle has them.
Recovery Hooks
{Warning
Never pull on recovery hooks from the
side. The hooks could break and you and
others could be injured. When using
recovery hooks, always pull the vehicle
from the front.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
228 Driving and Operating
cargo load should not exceed the truck's
cargo weight rating, and the camper's
center of gravity (1) should fall within
the truck's recommended center of
gravity zone (2) when installed.
Any accessories or other equipment
that are added to the vehicle must be
weighed. Then, subtract this extra
weight from the CWR. This extra weight
may shorten the center of gravity zone
of the vehicle.
If the slide-in camper and its load
weighs less than the CWR, the center of
gravity zone for the vehicle may be
larger.
Secure loose items to prevent weight
shifts that could affect the balance of
the vehicle. When the truck-camper is
loaded, drive to a scale and weigh on
the front and on the rear wheels
separately to determine axle loads.
Individual axle loads should not exceed
either of the gross axle weight ratings
(GAWR). The total axle loads should not
exceed the vehicle's gross vehicle
weight rating (GVWR). These ratings aregiven on the Certification/Tire label
attached to the B-pillar. See
“Certification/Tire Label”
underVehicle
Load Limits 0222. If weight ratings are
exceeded, move or remove items to
bring all weights below the ratings.
See your dealer for more information
on curb weights, cargo weights, Cargo
Weight Rating, and the correct center of
gravity zone.
Starting and Operating
New Vehicle Break-In
Caution
The vehicle does not need an elaborate
break-in. But it will perform better in the
long run if you follow these guidelines:
.Keep the vehicle speed at 88 km/h
(55 mph) or less for the first 805 km
(500 mi).
(Continued)
Caution (Continued)
.Do not drive at any one constant
speed, fast or slow, for the first
805 km (500 mi). Do not make
full-throttle starts. Avoid downshifting
to brake or slow the vehicle.
.Avoid making hard stops for the first
322 km (200 mi) or so. During this
time the new brake linings are not yet
broken in. Hard stops with new linings
can mean premature wear and earlier
replacement. Follow this breaking-in
guideline every time you get new
brake linings.
.Do not tow a trailer during break-in.
See Trailer Towing 0293 for the
trailer towing capabilities of the
vehicle and more information.
Following break-in, engine speed and load
can be gradually increased.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
240 Driving and Operating
N :In this position, the engine does not
connect with the wheels. To restart the
engine when the vehicle is already moving,
use N (Neutral) only.
Also, use N (Neutral) when the vehicle is
being towed.
{Warning
Shifting into a drive gear while the
engine is running at high speed is
dangerous. Unless your foot is firmly on
the brake pedal, the vehicle could move
very rapidly. You could lose control and
hit people or objects. Do not shift into a
drive gear while the engine is running at
high speed.
Caution
Shifting out of P (Park) or N (Neutral) with
the engine running at high speed may
damage the transmission. The repairs
would not be covered by the vehicle
warranty. Be sure the engine is not
running at high speed when shifting the
vehicle.
Caution
A transmission hot message may display
if the automatic transmission fluid is too
hot. Driving under this condition can
damage the vehicle. Stop and idle the
engine to cool the automatic
transmission fluid. This message clears
when the transmission fluid has cooled
sufficiently.
D : This position is for normal driving.
It provides the best fuel economy. If more
power is needed for passing, press the
accelerator pedal down.
.When going less than about 55 km/h (35
mph), push the accelerator pedal about
halfway down.
.When going about 55 km/h (35 mph) or
more, push the accelerator all the
way down.
By doing this, the vehicle shifts down to
the next gear and has more power.
Use D (Drive) and Tow/Haul Mode when
towing a trailer, carrying a heavy load,
driving on steep hills, or driving off-road.
Shift the transmission to a lower gear if the
transmission shifts too often. Downshifting the transmission in slippery
road conditions could result in skidding. See
“Skidding”
underLoss of Control 0215.
The vehicle has a shift stabilization feature
that adjusts the transmission shifting to the
current driving conditions in order to reduce
rapid upshifts and downshifts. This shift
stabilization feature is designed to
determine, before making an upshift, if the
engine is able to maintain vehicle speed by
analyzing things such as vehicle speed,
throttle position, and vehicle load. If the
shift stabilization feature determines that a
current vehicle speed cannot be maintained,
the transmission does not upshift and
instead holds the current gear. In some
cases, this could appear to be a delayed
shift, however the transmission is operating
normally.
The transmission uses adaptive shift
controls. The adaptive shift control process
continually compares key shift parameters
to pre-programmed ideal shifts stored in the
transmission’s computer. The transmission
constantly makes adjustments to improve
vehicle performance according to how the
vehicle is being used, such as with a heavy
load or when the temperature changes.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
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Driving and Operating 241
During this adaptive shift control process,
shifting might feel different as the
transmission determines the best settings.
When temperatures are very cold, the
transmission's gear shifting could be delayed
providing more stable shifts until the engine
warms up. Shifts could be more noticeable
with a cold transmission. This difference in
shifting is normal.
If equipped with the 2.7L L4 engine, engine
speeds may be increased while driving at
highway speeds while the engine is still
warming up.
L :This position allows selection of a range
of gears appropriate for current driving
conditions. If equipped, see “Range Selection
Mode” underManual Mode 0241.
Caution
Spinning the tires or holding the vehicle
in one place on a hill using only the
accelerator pedal may damage the
transmission. The repair will not be
covered by the vehicle warranty. If the
vehicle is stuck, do not spin the tires.
When stopping on a hill, use the brakes
to hold the vehicle in place.
Manual Mode
Electronic Range Select (ERS)
Caution
Driving with the engine at a high rpm
without upshifting while using Manual
Mode, could damage the vehicle. Always
upshift when necessary while using
Manual Mode.
Electronic Range Select (ERS), or Manual
Mode, allows for the selection of the range
of gear positions. Use this mode when
driving downhill or towing a trailer to limit
the top gear and vehicle speed. The shift
position indicator within the Driver
Information Center (DIC) will display a
number next to the L indicating the highest
available gear. To enter Electronic Range Select or
Manual Mode:
1. With the vehicle in D (Drive), pull back on the shift lever to activate L (Low). The
L in the shift pattern will illuminate in
red, and the D will switch to white.
2. Tap the left steering wheel control to reduce the highest gear available, or the
right control to increase the highest gear
available.
3. To exit, pull back on the shift lever a second time. The D in the shift pattern
will illuminate in red, and the L will
switch to white.
When shifting to L (Low), the transmission
will shift to a preset lower gear range. For
this preset range, the highest gear available
will be displayed next to the L in the DIC.
All gears below that number are available to
use. For example, when 4 (Fourth) is shown
next to the L, 1 (First) through 4 (Fourth)
gears are shifted automatically. To shift to 5
(Fifth) gear, tap the right steering wheel
control or shift into D (Drive).
L (Low) will prevent shifting to a lower gear
range if the engine speed is too high. If the
vehicle speed is not reduced within the time
allowed, the lower gear range shift will not

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
242 Driving and Operating
be completed. Slow the vehicle, then tap the
left steering wheel control to the desired
lower gear range.
Cruise control can be used while in ERS.
Tow/Haul Mode
The Tow/Haul Mode adjusts the
transmission shift pattern to reduce shift
cycling. This provides increased performance,
vehicle control, and enhanced transmission
and engine cooling when driving down steep
hills or mountain grades, when towing,
or when hauling heavy loads. SeeDriver
Mode Control 0251 to activate Tow/
Haul Mode.
For vehicles without Driver Mode Control,
press the Tow/Haul button on the center
stack.
If equipped, the Stop/Start system will
become unavailable when Tow/Haul Mode is
active.
If equipped with Active Hydraulic Assist, the
vehicle will provide a stiffer steering
response when Tow/Haul mode is engaged
to provide enhanced steering functionality.
Tow/Haul Mode Grade Braking
Tow/Haul Mode Grade Braking is only
enabled while the Tow/Haul Mode is
selected and the vehicle is not in the Range
Selection Mode. See Manual Mode0241.
Tow/Haul Mode Grade Braking assists in
maintaining desired vehicle speeds when
driving on downhill grades by using the
engine and transmission to slow the vehicle.
See Towing Equipment 0296.
Drive Systems
Four-Wheel Drive
If equipped, four-wheel drive engages the
front axle for extra traction. Read the appropriate section for transfer
case operation before using.
Caution
Do not drive on clean, dry pavement in
4
mand 4n(if equipped) for an extended
period of time. These conditions may
cause premature wear on the vehicle’s
powertrain.
Driving on clean, dry pavement in 4
mor
4
nmay:
.Cause a vibration to be felt in the
steering system.
.Cause tires to wear faster.
{Warning
If equipped with four-wheel drive, the
vehicle will be free to roll if the transfer
case is in N (Neutral), even when the shift
lever is in P (Park). You or someone else
could be seriously injured. Be sure the
transfer case is in a drive gear —2
m, 4m,
or 4
n— or set the parking brake before
placing the transfer case in N (Neutral).
See Shifting Into Park 0236.