2021 GMC SIERRA Owner's Manual

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
344 Vehicle Care
Stop/Start System
Vehicles equipped with a 2.7L L3B, 3.0L LM2,
5.3L L84 or 6.2L L87 are equipped with a
Stop/Start system to shut off the engine to
help conserve fuel. SeeStop/Start System
0 233.
Vehicles with the Stop/Start system have an
Absorbed Glass Mat (AGM) 12-volt battery.
Installation of a standard 12-volt battery will
result in reduced 12-volt battery life. When
using a 12-volt battery charger on the 12-volt
AGM battery, some chargers have an AGM
battery setting on the charger. If available,
use the AGM setting on the charger to limit
charge voltage to 14.8 volts. Follow the
charger manufacturer’s instructions.
{Warning
WARNING: Battery posts, terminals, and
related accessories contain lead and lead
compounds, chemicals known to the
State of California to cause cancer and
birth defects or other reproductive harm.
Batteries also contain other chemicals
known to the State of California to cause
cancer. WASH HANDS AFTER HANDLING.
(Continued)
Warning (Continued)
For more information go to
www.P65Warnings.ca.gov/
passenger-vehicle.
See California Proposition 65 Warning 0322
and the back cover.
Vehicle Storage
{Warning
Batteries have acid that can burn you and
gas that can explode. You can be badly
hurt if you are not careful. See Jump
Starting - North America 0391 for tips on
working around a battery without
getting hurt.
Infrequent Usage: Remove the black,
negative (−) cable from the battery to keep
the battery from running down.
Extended Storage: Remove the black,
negative (−) cable from the battery or use a
battery trickle charger.
Negative Battery Cable Disconnection
{Warning
Before disconnecting the negative battery
cable, turn off all features, turn the
ignition off, and remove the key,
if equipped, from the vehicle. If this is
not done, you or others could be injured,
and the vehicle could be damaged.
Caution
If the battery is disconnected with the
ignition on or the vehicle in Retained
Accessory Power (RAP), the OnStar
back-up battery will be permanently
discharged and will need to be replaced.
1. Make sure the lamps, features, and accessories are turned off.
2. Turn the ignition off and remove the key, if equipped.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Vehicle Care 345
For vehicles equipped with the Stop/Start
system:
1. Loosen and remove the negative batterycable nut (1) at the battery sensor
connection.
2. Remove the negative battery cable (2) from the battery sensor stud.
3. Cover the negative battery cable terminal, battery sensor stud, and
negative battery post with a
non-conductive material to prevent any
contact with the negative battery cable. For vehicles not equipped with the Stop/
Start system:1. Loosen the negative battery cable nut (1).
2. Remove the negative battery cable
clamp (2) from the negative battery post.
3. Cover the negative battery cable clamp, and negative battery post with a
non-conductive material to prevent any
contact with the negative battery cable.
Negative Battery Cable Reconnection
Caution
When reconnecting the battery:
.Use the original nut from the vehicle
to secure the negative battery cable.
Do not use a different nut. If you
need a replacement nut, see your
dealer.
.Tighten the nut with a hand tool. Do
not use an impact wrench or power
tools to tighten the nut.
The vehicle could be damaged if these
guidelines are not followed.
Caution
Do not use paints, lubricants, or corrosion
inhibitors on the nut that secures the
negative battery cable to the vehicle. This
could damage the vehicle.
For vehicles equipped with the Stop/Start
system: 1. Install the negative battery cable to the battery sensor stud.
2. Install the negative battery cable nut to the battery sensor stud and tighten.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
346 Vehicle Care
3. Turn the ignition on.
For vehicles not equipped with the Stop/
Start system: 1. Install the negative battery cable clamp to the negative battery post.
2. Tighten the negative battery cable nut.
3. Turn the ignition on.
Four-Wheel Drive
Transfer Case
When to Check Lubricant
Refer to Maintenance Schedule 0409 to
determine when to check the lubricant.
1. Fill Plug
2. Drain Plug
To get an accurate reading, the vehicle
should be on a level surface.
If the level is below the bottom of the fill
plug (1) hole, located on the transfer case,
some lubricant will need to be added. Add
enough lubricant to raise the level to the
bottom of the fill plug (1) hole. Use care not
to overtighten the plug.
When to Change Lubricant
Refer to Maintenance Schedule 0409 to
determine how often to change the
lubricant.
What to Use
Refer to Recommended Fluids and Lubricants
0 418 to determine what kind of lubricant
to use.
Front Axle
When to Check Lubricant
It is not necessary to regularly check the
front axle fluid unless a leak is suspected or
an unusual noise is heard. A fluid loss could
indicate a problem. Have it inspected and
repaired. This service can be complex. See
your dealer. Do not directly power wash the transfer
case and/or front/rear axle output seals.
High pressure water can overcome the seals
and contaminate the fluid. Contaminated
fluid will decrease the life of the transfer
case and/or drive axles and should be
replaced.
Rear Axle
When to Check Lubricant
It is not necessary to regularly check the
rear axle fluid unless a leak is suspected or
an unusual noise is heard. A fluid loss could
indicate a problem. Have it inspected and
repaired. This service can be complex. See
your dealer.
Do not directly power wash the transfer
case and/or front/rear axle output seals.
High pressure water can overcome the seals
and contaminate the fluid. Contaminated
fluid will decrease the life of the transfer
case and/or drive axles and should be
replaced.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Vehicle Care 347
Starter Switch Check
{Warning
When you are doing this inspection, the
vehicle could move suddenly. If the
vehicle moves, you or others could be
injured.
1. Before starting this check, be sure there is enough room around the vehicle.
2. Apply both the parking brake and the regular brake.
Do not use the accelerator pedal, and be
ready to turn off the engine immediately
if it starts.
3. Try to start the engine in each gear. The vehicle should start only in P (Park) or
N (Neutral). If the vehicle starts in any
other position, contact your dealer for
service.
Automatic Transmission Shift Lock
Control Function Check
{Warning
When you are doing this inspection, the
vehicle could move suddenly. If the
vehicle moves, you or others could be
injured.
1. Before starting this check, be sure there is enough room around the vehicle.
It should be parked on a level surface.
2. Apply the parking brake. Be ready to apply the regular brake immediately if
the vehicle begins to move.
3. With the engine off, turn the ignition on, but do not start the engine. Without
applying the regular brake, try to move
the shift lever out of P (Park) with
normal effort. If the shift lever moves
out of P (Park), contact your dealer for
service.
Ignition Transmission Lock Check
If equipped with Key Access ignition, while
parked, and with the parking brake set, try
to turn the ignition off in each shift lever
position. The ignition should turn to off only
when the shift lever is in P (Park).
The ignition key should come out only when
the ignition is off. Contact your dealer if
service is required.
Park Brake and P (Park)
Mechanism Check
{Warning
When you are doing this check, the
vehicle could begin to move. You or
others could be injured and property
could be damaged. Make sure there is
room in front of the vehicle in case it
begins to roll. Be ready to apply the
regular brake at once should the vehicle
begin to move.
Park on a fairly steep hill, with the vehicle
facing downhill. Keeping your foot on the
regular brake, set the parking brake.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
348 Vehicle Care
.To check the parking brake's holding
ability: With the engine running and the
transmission in N (Neutral), slowly remove
foot pressure from the regular brake
pedal. Do this until the vehicle is held by
the parking brake only.
.To check the P (Park) mechanism's holding
ability: With the engine running, shift to
P (Park). Then release the parking brake
followed by the regular brake.
Contact your dealer if service is required.
Wiper Blade Replacement
Windshield wiper blades should be replaced
periodically. See Maintenance Schedule
0 409.
Replacement blades come in different types
and are removed in different ways. For
proper type and length, see Maintenance
Replacement Parts 0419.
Caution
Allowing the wiper arm to touch the
windshield when no wiper blade is
installed could damage the windshield.
Any damage that occurs would not be
(Continued)
Caution (Continued)
covered by the vehicle warranty. Do not
allow the wiper arm to touch the
windshield.
Front Wiper Blade Replacement
To replace the wiper blade:
1. Pull the wiper assembly away from the windshield.
2. Lift up on the latch in the middle of the
wiper blade where the wiper arm
attaches. 3. With the latch open, pull the wiper blade
down toward the windshield far enough
to release it from the J-hooked end of
the wiper arm.
4. Remove the wiper blade.
5. Reverse Steps 1–3 for wiper blade replacement.
Glass Replacement
If the windshield or front side glass must be
replaced, see your dealer to determine the
correct replacement glass.
Windshield Replacement
HUD System
The windshield is part of the HUD system.
If the windshield must be replaced, get one
that is designed for HUD or the HUD image
may look out of focus.
Driver Assistance Systems
If the windshield needs to be replaced and
the vehicle is equipped with a front camera
sensor for the Driver Assistance Systems, a
GM replacement windshield is
recommended. The replacement windshield
must be installed according to GM
specifications for proper alignment. If it is

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Vehicle Care 349
not, these systems may not work properly,
they may display messages, or they may
not work at all. See your dealer for proper
windshield replacement.
Gas Strut(s)
This vehicle is equipped with gas strut(s) to
provide assistance in lifting and holding
open the hood/trunk/liftgate system in full
open position.
{Warning
If the gas struts that hold open the hood,
trunk, and/or liftgate fail, you or others
could be seriously injured. Take the
vehicle to your dealer for service
immediately. Visually inspect the gas
struts for signs of wear, cracks, or other
damage periodically. Check to make sure
the hood/trunk/liftgate is held open with
enough force. If struts are failing to hold
the hood/trunk/liftgate, do not operate.
Have the vehicle serviced.
Caution
Do not apply tape or hang any objects
from gas struts. Also do not push down
or pull on gas struts. This may cause
damage to the vehicle.
See Maintenance Schedule 0409.
Hood
Trunk
Liftgate

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
350 Vehicle Care
Headlamp Aiming
Front Headlamp Aiming
Headlamp aim has been preset and should
need no further adjustment.
If the vehicle is damaged in a crash, the
headlamp aim may be affected.
If adjustment to the headlamps is necessary,
see your dealer.
Bulb Replacement
For the proper type of replacement bulbs,
or any bulb changing procedure not listed in
this section, contact your dealer.
Caution
Do not replace incandescent bulbs with
aftermarket LED replacement bulbs. This
can cause damage to the vehicle electrical
system.
Halogen Bulbs
{Warning
Halogen bulbs have pressurized gas inside
and can burst if you drop or scratch the
bulb. You or others could be injured. Be
sure to read and follow the instructions
on the bulb package.
LED Lighting
This vehicle has several LED lamps. For
replacement of any LED lighting assembly,
contact your dealer.
Headlamps, Front Turn Signal,
Sidemarker, and Parking Lamps
Base Level Headlamp Assembly
1. Turn Signal Lamps
Headlamp Replacement
See your dealer for headlamp replacement.
Turn Signal Lamp Replacement
Base Level1. Open the hood.
2. Turn the bulb socket counterclockwise to remove it from the headlamp assembly
and pull it straight out.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
Vehicle Care 351
3. Remove the bulb by pulling it straightout of the bulb socket.
4. Replace the bulb and reverse Steps 1–3 to reinstall.
Uplevel
See your dealer for headlamp replacement.
Taillamps, Turn Signal, Stoplamps,
and Back-Up Lamps
Base Level Taillamp Assembly
1. Stoplamp/Turn Signal Lamp
2. Back-Up Lamp
Uplevel Taillamp Assembly
See your dealer for taillamp replacement.
It is recommended to replace the grommets
when replacing a bulb. See your dealer.
To replace one of these bulbs: 1. Open the tailgate.
2. Remove the two rear lamp assembly screws.
4. Pull the rear lamp assembly outward andrearward away from the box side to
remove it from the vehicle.
5. Turn the bulb socket counterclockwise.
6. Pull the bulb straight out from the socket.
7. Replace the bulb and reverse Steps 1–5 to reinstall.