ECU GMC SIERRA 2018 Repair Manual

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
328 Driving and Operating
Caution
Leaving electrical equipment on
for extended periods will drain the
battery. Always turn off electrical
equipment when not in use and
do not use equipment that
exceeds the maximum amperage
rating of 30 amps for the auxiliary
battery provision.
Trailer Wiring Harness
The vehicle is equipped with one of
the following wiring harnesses for
towing a trailer or hauling a slide-in
camper.
Basic Trailer Wiring
All regular, double cab, and crew
cab pickups have a seven-wire
trailer towing harness.
For vehicles not equipped with
heavy-duty trailering, the harness is
secured to the vehicle's frame
behind the spare tire mount. 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:
.
Green/Violet: Right Stop/Turn
Signal
. Yellow/Gray: Left Stop/Turn
Signal
. Gray/Brown: Taillamps/Parking
Lamps
. White/Green: Back-up Lamps
. Red/Green: Battery Feed
. White: Ground
. Blue: Electric Trailer Brake
The fuse for the electric trailer brake
circuit is installed in the underhood
electrical center, but the wires may
not be connected. They should be
connected by your dealer or a
qualified service center. To control
electric trailer brakes, a trailer brake
controller needs to be installed on
the vehicle by your dealer or a qualified service center, see
“Electric Brake Control Wiring
Provisions”
later in this section.
Heavy-Duty Trailer Wiring Harness
Package
For vehicles equipped with
heavy-duty trailering, the harness
connector is mounted in the bumper.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
338 Driving and Operating
.Make sure the weight on the
front and rear axles does not
exceed the axle rating for each.
. For the front axle, if more cargo
or passengers must be carried,
appropriate counter ballast must
be installed rear of the rear axle.
Counter ballast must be properly
secured so it will not move
during driving.
. Rear ballast may be required to
ensure a proper front and rear
weight distribution ratio, even
though the actual weight at the
front axle may be less than the
front axle rating.
. The snow plow manufacturer or
installer can assist in
determining the amount of rear
ballast required, to help make
sure the snow plow/vehicle
combination does not exceed
the GVW rating, the front and
rear axle ratings, and the front
and rear weight distribution ratio.
. The total vehicle must not
exceed the GVW rating. Front axle reserve capacity is the
difference between the Gross Axle
Weight Rating (GAWR) and the front
axle weight of the vehicle with full
fuel and passengers. This is the
amount of weight that can be added
to the front axle before reaching the
front GAWR.
United States
Canada
The front axle reserve capacity for
the vehicle is in the lower right
corner of the Certification/Tire label.
To calculate the amount of weight
any front accessory, such as a snow
plow, is adding to the front axle, use
this formula:

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
Vehicle Care 363
6. Verify coolant level after theengine is shut off and the
coolant is cold. If necessary,
repeat coolant fill procedure
Steps 1–6.
Caution
If the pressure cap is not tightly
installed, coolant loss and engine
damage may occur. Be sure the
cap is properly and tightly
secured.
Engine Overheating
If the vehicle has the Duramax
diesel engine, see the Duramax
diesel supplement.
Caution
Do not run the engine if there is a
leak in the engine cooling system.
This can cause a loss of all
coolant and can damage the
system and vehicle. Have any
leaks fixed right away. The vehicle has several indicators
to warn of engine overheating.
There is a coolant temperature
gauge in the vehicle's instrument
cluster. See
Engine Coolant
Temperature Gauge 0144.
In addition, there are ENGINE
OVERHEATED STOP ENGINE,
ENGINE OVERHEATED IDLE
ENGINE, and ENGINE POWER IS
REDUCED messages in the Driver
Information Center (DIC).
If the decision is made not to lift the
hood when this warning appears,
get service help right away. See
Roadside Assistance Program
0 469.
If the decision is made to lift the
hood, make sure the vehicle is
parked on a level surface.
4.3L V6, 5.3L V8, and 6.2L
V8 Engines
Check to see if the engine cooling
fans are running. If the engine is
overheating, the fans should be running. If they are not, do not
continue to run the engine and have
the vehicle serviced.
If Steam is Coming from the
Engine Compartment
{Warning
Steam and scalding liquids from a
hot cooling system are under
pressure. Turning the pressure
cap, even a little, can cause them
to come out at high speed and
you could be burned. Never turn
the cap when the cooling system,
including the pressure cap, is hot.
Wait for the cooling system and
pressure cap to cool.
If No Steam is Coming from
the Engine Compartment
The ENGINE OVERHEATED STOP
ENGINE or the ENGINE
OVERHEATED IDLE ENGINE
message, along with a low coolant
condition, can indicate a serious
problem.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
Vehicle Care 413
Tire Chains
{Warning
If the vehicle has dual wheels or
265/65R18, P265/65R18,
P275/55R20, LT265/70R17,
LT265/70R18, LT265/60R20,
LT275/65R18, P285/50R20,
285/45R22, or P285/45R22 size
tires, do not use tire chains. They
can damage the vehicle because
there is not enough clearance.
Tire chains used on a vehicle
without the proper amount of
clearance can cause damage to
the brakes, suspension, or other
vehicle parts. The area damaged
by the tire chains could cause you
to lose control of the vehicle and
you or others may be injured in a
crash.
Use another type of traction
device only if its manufacturer
recommends it for use on the
vehicle and tire size combination(Continued)
Warning (Continued)
and road conditions. Follow that
manufacturer's instructions. To
help avoid damage to the vehicle,
drive slowly, readjust, or remove
the device if it is contacting the
vehicle, and do not spin the
vehicle's wheels.
If you do find traction devices that
will fit, install them on the rear
tires.
Caution
If the vehicle does not have dual
wheels and has a tire size other
than 265/65R18, P265/65R18,
P275/55R20, LT265/70R17,
LT265/70R18, LT265/60R20,
LT275/65R18, P285/50R20,
285/45R22, or P285/45R22, use
tire chains only where legal and
only when you must. Use chains
that are the proper size for the(Continued)
Caution (Continued)
tires. Install them on the tires of
the rear axle. Do not use chains
on the tires of the front axle.
Tighten them as tightly as
possible with the ends securely
fastened. Drive slowly and follow
the chain manufacturer's
instructions. If you can hear the
chains contacting the vehicle,
stop and retighten them. If the
contact continues, slow down
until it stops. Driving too fast or
spinning the wheels with chains
on will damage the vehicle.
If a Tire Goes Flat
It is unusual for a tire to blowout
while driving, especially if the tires
are maintained properly. If air goes
out of a tire, it is much more likely to
leak out slowly. But if there ever is a
blowout, here are a few tips about
what to expect and what to do:

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
420 Vehicle Care
Rear Position–All Other Models
For all other models, position
the jack under the rear axle
between the spring anchor and
the shock absorber bracket.
If a snow plow has been added
to the front of the vehicle, lower
the snow plow fully before
raising the vehicle.
Make sure that the jack head is
positioned so that the rear axle
is resting securely between the
grooves that are on the
jack head.
{Warning
Getting under a vehicle when it is
lifted on a jack is dangerous.
If the vehicle slips off the jack,
you could be badly injured or
killed. Never get under a vehicle
when it is supported only by
a jack.
{Warning
Raising the vehicle with the jack
improperly positioned can
damage the vehicle and even
make the vehicle fall. To help
avoid personal injury and vehicle
damage, be sure to fit the jack lift
head into the proper location
before raising the vehicle.
6. Turn the wheel wrench clockwise to raise the vehicle.
Raise the vehicle far enough
off the ground so there is
enough room for the spare tire
to fit under the wheel well.
7. Remove all the wheel nuts andtake off the flat tire.
{Warning
Rust or dirt on a wheel, or on the
parts to which it is fastened, can
make wheel nuts become loose
after time. The wheel could come
off and cause an accident. When
changing a wheel, remove any
rust or dirt from places where the
wheel attaches to the vehicle. In
an emergency, a cloth or a paper
(Continued)

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
424 Vehicle Care
3. Attach the wheel wrench (7)and extensions (6) together, as
shown.
4. Insert the hoist end (10)
through the hole (9) in the rear
bumper and onto the hoist
shaft.
Do not use the chiseled end of
the wheel wrench.
5. Raise the tire part way upward. Make sure the retainer is
seated in the wheel opening. 6. Raise the tire fully against the
underside of the vehicle by
turning the wheel wrench
clockwise until you hear two
clicks or feel it skip twice. You
cannot overtighten the cable.
7. Make sure the tire is storedsecurely. Push, pull, and then
try to turn the tire. If the tire
moves, use the wheel wrench
to tighten the cable.
8. Reinstall the spare tire lock, if the vehicle has one. To store the jack and jack tools:
1. Wing Nut Retaining Wheel
Blocks
2. Wheel Blocks
3. Wing Nut Retaining Tool Kit
4. Wheel Wrench and Extensions
5. Tool Bag
6. Jack Mounting Bracket
7. Jack
8. Bolt Retaining Wheel Blocks
1. Put the tools (4) in the tool bag (5) and place them in the
retaining bracket (3).
2. Tighten down the wing nut (3).

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
430 Vehicle Care
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.
Towing the Vehicle
Caution
Incorrectly towing a disabled
vehicle may cause damage. The
damage would not be covered by
the vehicle warranty.
Do not lash or hook to
suspension components. Use the
proper straps around the tires to
secure the vehicle.
Use only a flatbed tow truck for
towing a disabled vehicle. Never
use a sling type lift or damage will
occur. Use ramps to help reduce
approach angles if necessary.
A towed vehicle should have its
drive wheels off the ground.
Consult a professional towing
service if the disabled vehicle must
be towed.
Front Attachment Points
The vehicle is equipped with
specific attachment points to be
used to pull the vehicle onto a
flatbed car carrier from a flat road
surface. Do not use these
attachment points to pull the vehicle
from snow, mud or sand.
Recreational Vehicle
Towing
Recreational vehicle towing means
towing the vehicle behind another
vehicle, such as a motor home. The
two most common types of

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
432 Vehicle Care
Warning (Continued)
be injured. Set the parking brake
before shifting the transfer case
to N (Neutral).
To dinghy tow: 1. Position the vehicle being towed behind the tow vehicle,
facing forward and on a level
surface.
2. Securely attach the vehicle being towed to the tow vehicle.
3. Apply the parking brake and start the engine.
4. Shift the transfer case to N (Neutral). See “Shifting into
N (Neutral)” underFour-Wheel
Drive 0272. Check that the
vehicle is in N (Neutral) by
shifting the transmission to
R (Reverse) and then to D
(Drive). There should be no
movement of the vehicle while
shifting.
5. Turn the engine off.
Caution
Failure to disconnect the negative
battery cable or to have it contact
the terminals can cause damage
to the vehicle.
6. Disconnect the negative battery cable at the battery and
secure the nut and bolt. Cover
the negative battery post with a
non-conductive material to
prevent any contact with the
negative battery terminal.
7. Shift the transmission to P (Park).
Caution
If the steering column is locked,
vehicle damage may occur.
8. Move the steering wheel to make sure the steering column
is unlocked. 9. With a foot on the brake pedal,
release the parking brake.
Keep the ignition key in the
towed vehicle in ACC/
ACCESSORY to prevent the
steering column from locking.
Disconnecting the Towed Vehicle
Before disconnecting the towed
vehicle: 1. Park on a level surface.
2. Set the parking brake, then shift the transmission to
P (Park), and turn the ignition
key off.
3. Connect the battery.
4. Apply the brake pedal.
5. Turn the ignition on with the engine off. Shift the transfer
case out of N (Neutral) to
Two-Wheel Drive High. See
“Shifting out of N (Neutral)”
under Four-Wheel Drive 0272.
See your dealer if the transfer
case cannot be shifted out of
N (Neutral).

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
434 Vehicle Care
To dolly tow a four-wheel-drive
vehicle from the front:1. Attach the dolly to the tow vehicle following the dolly
manufacturer's instructions.
2. Drive the front wheels onto the dolly.
3. Shift the transmission to P (Park).
4. Set the parking brake.
{Warning
Shifting a four-wheel-drive
vehicle's transfer case into
N (Neutral) can cause the vehicle
to roll even if the transmission is
in P (Park). You or others could
be injured. Set the parking brake
before shifting the transfer case
to N (Neutral). 5. Use a clamping device
designed for towing to ensure
that the front wheels are locked
into the straight position.
6. Secure the vehicle to the dolly following the manufacturer's
instructions.
7. Shift the transfer case to N (Neutral). See “Shifting into
N (Neutral)” underFour-Wheel
Drive 0272 for the proper
procedure.
8. Release the parking brake only after the vehicle being towed is
firmly attached to the tow
vehicle.
9. Turn the ignition off.
Rear Towing (Rear Wheels Off
the Ground)
Two-Wheel-Drive Vehicles
To dolly tow a two-wheel-drive
vehicle from the rear: 1. Drive the rear wheels onto the dolly.
2. Set the parking brake. See Parking Brake 0281.
3. Put the transmission in P (Park).
4. Secure the vehicle to the dolly following the manufacturer's
instructions.

GMC Sierra/Sierra Denali Owner Manual (GMNA-Localizing-U.S./Canada/
Mexico-11349177) - 2018 - CRC - 10/17/17
Vehicle Care 435
5. Use a clamping devicedesigned for towing to ensure
that the front wheels are locked
into the straight position.
6. Turn the ignition off.
Four-Wheel-Drive Vehicles
{Warning
Shifting a four-wheel-drive
vehicle's transfer case into
N (Neutral) can cause the vehicle
to roll even if the transmission is
in P (Park). You or others could
be injured. Set the parking brake
before shifting the transfer case
to N (Neutral). To dolly tow a four-wheel-drive
vehicle from the rear:
1. Drive the rear wheels onto the dolly.
2. Set the parking brake. See Parking Brake 0281.
3. Put the transmission in P (Park).
4. Secure the vehicle to the dolly following the manufacturer's
instructions.
5. Use a clamping device designed for towing to ensure
that the front wheels are locked
into the straight position.
6. Shift the transfer case to N (Neutral). See “Shifting into
N (Neutral)” underFour-Wheel
Drive 0272 for the proper
procedure.
7. Turn the ignition off.
Appearance Care
Exterior Care
Locks
Locks are lubricated at the factory.
Use a de-icing agent only when
absolutely necessary, and have the
locks greased after using. See
Recommended Fluids and
Lubricants 0456.
Washing the Vehicle
To preserve the vehicle's finish,
wash it often and out of direct
sunlight.
{Warning
Do not power wash any part of
the vehicle’s interior, including the
vinyl floor covering. This could
damage safety and other systems
in the vehicle, which would not be
covered by the vehicle warranty.