
GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./
Canada/Mexico-14632426) - 2021 - CRC - 11/5/20
264 Driving and Operating
Weather Conditions Affecting ACC
If the interior temperature is extremely
high, the instrument cluster may indicate
that ACC is temporarily unavailable. This can
be caused by extreme hot weather
conditions with direct sunlight on the front
camera. ACC will return to normal operation
once the cabin temperature is lower.
Conditions that are associated with low
visibility, such as fog, rain, snow, or road
spray, may limit ACC performance. Water
droplets from rain or snow that remain on
the windshield may also limit ACC’s ability
to detect objects.
{Warning
Camera visibility may be limited and the
ACC system may not work properly if the
windshield is not clear. Do not use ACC if
moisture is present on the inside of the
windshield or the windshield washer is
used in cold weather. Turn on the front
defroster and make sure the windshield is
clear before using ACC. Before driving,
check that the windshield wipers are in
good condition and replace them if worn.Lighting Conditions Affecting ACC
The ACC front camera can be affected by
poor lighting conditions, and ACC may have
limited performance when:
.There are changes in brightness, such as
entering and exiting tunnels, bridges, and
overpasses.
.Low sun angles cause the camera to not
detect objects, or it is more difficult to
detect objects in the same traffic lane.
.Lighting is poor in the evening or early
morning
.There are multiple changes in brightness
or shadows along the vehicle roadway.
.In a tunnel without the headlamps on,
or in a tunnel when there is a vehicle in
front that does not have its taillamps on.
.Subjected to strong light from opposing
lane traffic in the front of the vehicle,
such as high-beam headlamps from
oncoming traffic.
Accessory Installations and Vehicle
Modifications
Do not install or place any object around
the front camera windshield area that would
obstruct the front camera view. Do not install objects on top of the vehicle
that overhang and obstruct the front
camera, such as a canoe, kayak, or other
items that can be transported on the
vehicle roof.
Do not modify the hood, headlamps, or fog
lamps, as this may limit the camera’s ability
to detect an object.
Cleaning the Sensing System
The camera sensor on the windshield behind
the rearview mirror can become blocked by
snow, ice, dirt, mud, or debris. This area
needs to be cleaned for ACC to operate
properly.
The vehicle headlamps may need to be
cleaned due to dirt, snow, or ice. Objects
that are not illuminated correctly may be
difficult to detect.
If ACC will not operate, regular cruise control
may be available. See
“Switching Between
ACC and Regular Cruise Control” previously
in this section. Always consider driving
conditions before using either cruise control
system.
For cleaning instructions, see “Washing the
Vehicle” underExterior Care 0398.

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./Cana-
da/Mexico-14632426) - 2021 - CRC - 11/5/20
Index 453
H
Halogen Bulbs . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
Hazard Warning Flashers . . . . . . . . . . . . . . . . .142
HD Radio Technology . . . . . . . . . . . . . . . . . . . . 156
Head Restraints . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Head-up Display . . . . . . . . . . . . . . . . . . . . . . . . . .128
HeadlampsAiming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
Automatic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
Bulb Replacement . . . . . . . . . . . . . . . . . . . . . . 350
Daytime Running Lamps (DRL) . . . . . . . . . . 141
Flash-to-Pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Headlamps, Front Turn Signal,Sidemarker, and Parking Lamps . . . . . . 350
High-Beam On Light . . . . . . . . . . . . . . . . . . . 123
High/Low Beam Changer . . . . . . . . . . . . . . . 141
Lamps On Reminder . . . . . . . . . . . . . . . . . . . 123
Heated Rear Seats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Steering Wheel . . . . . . . . . . . . . . . . . . . . . . . . 100
Heated and Ventilated Front Seats . . . . . . . .52
Heated Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Heater Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
Heating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204, 206
High-Beam On Light . . . . . . . . . . . . . . . . . . . . . . 123
Hill and Mountain Roads . . . . . . . . . . . . . . . . 219
Hill Descent Control (HDC) . . . . . . . . . . . . . . . 250 Hill Descent Control Light . . . . . . . . . . . . . . . . . 119
Hill Start Assist (HSA) . . . . . . . . . . . . . . . . . . . . 248
Hood . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
Horn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
How to Wear Seat Belts Properly . . . . . . . . . .55
HVAC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204, 206
I
If the System Needs Service . . . . . . . . . . . . . . 175
Ignition Positions . . . . . . . . . . . . . . . . . . . 229, 230
Ignition Transmission Lock Check . . . . . . . . 347
Immobilizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Indicator
Pedestrian Ahead . . . . . . . . . . . . . . . . . . . . . . . 119
Vehicle Ahead . . . . . . . . . . . . . . . . . . . . . . . . . . 119
Infants and Young Children, Restraints . . . . .72
Information Publication Ordering . . . . . . . . . . . . . . . . . . . 435
Infotainment System . . . . . . . . . . . . . . . . . . . . 439
Instrument Cluster . . . . . . . . . . . . . . . . . . . . . . . 106
Instrument Panel Overview . . . . . . . . . . . . . . . . 4
Interior Rearview Mirrors . . . . . . . . . . . . . . . . . 38
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1, 148
J
Jack Auxiliary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
Jump Starting - North America . . . . . . . . . . . 391
K
Keyless Entry Remote (RKE) System . . . . . . . . . . . . . . . . 10, 13
Keys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7, 9
L
Labeling, Tire Sidewall . . . . . . . . . . . . . . . . . . . 362
Lamps Auxiliary Roof Mounted Lamp . . . . . . . . . 144
Daytime Running (DRL) . . . . . . . . . . . . . . . . . 141
Dome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
Exterior Cargo . . . . . . . . . . . . . . . . . . . . . . . . . 144
Exterior Controls . . . . . . . . . . . . . . . . . . . . . . . 139
Exterior Lamps Off Reminder . . . . . . . . . . . 141
Exterior Lighting Battery Saver . . . . . . . . 147
License Plate . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
Malfunction Indicator (CheckEngine) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
On Reminder . . . . . . . . . . . . . . . . . . . . . . . . . . 123
Reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Lane Change Alert (LCA) . . . . . . . . . . . . . . . . . 280
Lane Keep Assist (LKA) . . . . . . . . . . . . . . . . . . . .281
Lane Keep Assist Light . . . . . . . . . . . . . . . . . . . . 119
Lap-Shoulder Belt . . . . . . . . . . . . . . . . . . . . . . . . . .57
LATCH System Replacing Parts after a Crash . . . . . . . . . . . 88
LATCH, Lower Anchors and Tethers for Children . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77

GMC Sierra/Sierra Denali 1500 Owner Manual (GMNA-Localizing-U.S./Cana-
da/Mexico-14632426) - 2021 - CRC - 11/5/20
454 Index
LED Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
LightingEntry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
Illumination Control . . . . . . . . . . . . . . . . . . . 145
LED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
Task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
Lights Airbag Readiness . . . . . . . . . . . . . . . . . . . . . . . 114
Antilock Brake System (ABS)Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
Brake System Warning . . . . . . . . . . . . . . . . . 117
Charging System . . . . . . . . . . . . . . . . . . . . . . . 115
Check Engine (Malfunction Indicator) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Cruise Control . . . . . . . . . . . . . . . . . . . . . . . . . 123
Door Ajar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
Driver Mode Control . . . . . . . . . . . . . . . . . . . . 121
Electric Parking Brake . . . . . . . . . . . . . . . . . . . 117
Electronic Stability Control (ESC), Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Engine Coolant Temperature Warning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
Engine Oil Pressure . . . . . . . . . . . . . . . . . . . . 122
Flash-to-Pass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141
Four-Wheel-Drive . . . . . . . . . . . . . . . . . . . . . . . 118
Front Fog Lamp . . . . . . . . . . . . . . . . . . . . . . . . 123
High-Beam On . . . . . . . . . . . . . . . . . . . . . . . . . 123 Lights (cont'd)
High/Low Beam Changer . . . . . . . . . . . . . . . 141
Hill Descent Control . . . . . . . . . . . . . . . . . . . . 119
Lane Keep Assist . . . . . . . . . . . . . . . . . . . . . . . . 119
Low Fuel Warning . . . . . . . . . . . . . . . . . . . . . 122
Seat Belt Reminders . . . . . . . . . . . . . . . . . . . . 113
Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Service Electric Parking Brake . . . . . . . . . . . 118
Tire Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
Tow/Haul Mode . . . . . . . . . . . . . . . . . . . . . . . . 119
Traction Off . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
Limited-Slip Differential . . . . . . . . . . . . . . . . . . 254
Lock
Steering Column . . . . . . . . . . . . . . . . . . . . . . . . 32
Locking Rear Axle . . . . . . . . . . . . . . . . . . . . . . . . 254
Locks Automatic Door . . . . . . . . . . . . . . . . . . . . . . . . . 22
Delayed Locking . . . . . . . . . . . . . . . . . . . . . . . . 22
Door . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Lockout Protection . . . . . . . . . . . . . . . . . . . . . . 22
Power Door . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Loss of Control . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
Low Fuel Warning Light . . . . . . . . . . . . . . . . . . 122
Lower Anchors and Tethers for Children (LATCH System) . . . . . . . . . . . . . . . . .77
Lumbar Adjustment . . . . . . . . . . . . . . . . . . . . . . . 48 Front Seats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48M
MaintenanceRecords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
Maintenance and Care Additional . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
Maintenance Schedule . . . . . . . . . . . . . . . . . . . 409 Recommended Fluids andLubricants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Transfer Case . . . . . . . . . . . . . . . . . . . . . . . . . . 242
Malfunction Indicator Lamp . . . . . . . . . . . . . . . 115
Manual Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Manual Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . .241
Manual Windows . . . . . . . . . . . . . . . . . . . . . . . . . .41
Map Data Updates . . . . . . . . . . . . . . . . . . . . . . . . 175
Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
Media
Avoiding Untrusted Devices . . . . . . . . . . . . 158
Memory Seats . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Messages Engine Power . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Vehicle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
Vehicle Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Mirror Rear Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Mirrors Automatic Dimming . . . . . . . . . . . . . . . . . . . . 37
Automatic Dimming Rearview . . . . . . . . . . 38
Blind Spot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37