Page 1 of 578

Seats and Restraint Systems........................... 1-1
Front Seats
............................................... 1-3
Rear Seats
..............................................1-12
Safety Belts
.............................................1-14
Child Restraints
.......................................1-35
Airbag System
.........................................1-68
Restraint System Check
............................1-87
Features and Controls..................................... 2-1
Keys
........................................................ 2-3
Doors and Locks
......................................2-10
Windows
.................................................2-15
Theft-Deterrent Systems
............................2-18
Starting and Operating Your Vehicle
...........2-22
Mirrors
....................................................2-55
Object Detection Systems
..........................2-63
OnStar
®System
......................................2-65
Universal Home Remote System
................2-68
Storage Areas
.........................................2-74
Sunroof
..................................................2-79
Instrument Panel............................................. 3-1
Instrument Panel Overview
.......................... 3-4
Climate Controls
......................................3-25
Warning Lights, Gages, and Indicators
........3-34
Driver Information Center (DIC)
..................3-54
Audio System(s)
.......................................3-80Driving Your Vehicle....................................... 4-1
Your Driving, the Road, and Your Vehicle
..... 4-2
Towing
...................................................4-50
Service and Appearance Care.......................... 5-1
Service
..................................................... 5-4
Fuel
......................................................... 5-6
Checking Things Under the Hood
...............5-12
Rear Axle
...............................................5-51
Four-Wheel Drive
.....................................5-52
Front Axle
...............................................5-54
Noise Control System
...............................5-56
Headlamp Aiming
.....................................5-56
Bulb Replacement
....................................5-59
Windshield Wiper Blade Replacement
.........5-65
Tires
......................................................5-66
Appearance Care
...................................5-112
Vehicle Identi cation
...............................5-121
Electrical System
....................................5-122
Capacities and Speci cations
...................5-130
Maintenance Schedule..................................... 6-1
Maintenance Schedule
................................ 6-2
Customer Assistance Information.................... 7-1
Customer Assistance and Information
........... 7-2
Reporting Safety Defects
...........................7-14
Vehicle Data Recording and Privacy
...........7-16
Index................................................................ 1
2008 GMC Sierra Owner ManualM
Page 32 of 578

Lap-Shoulder Belt
All seating positions in your vehicle have a lap-shoulder
belt except for the center front passenger position (if
equipped) if your vehicle is a crew or extended
cab, which has a lap belt. SeeLap Belt (Crew and
Extended Cab) on page 1-34for more information.
Here is how to wear a lap-shoulder belt properly.
1. Adjust the seat, if the seat is adjustable, so you can
sit up straight. To see how, see “Seats” in the Index.
2. Pick up the latch plate and pull the belt across you.
Do not let it get twisted.
The lap-shoulder belt may lock if you pull the belt
across you very quickly. If this happens, let the belt
go back slightly to unlock it. Then pull the belt
across you more slowly.
If you ever pull the shoulder portion of a passenger
belt out all the way, you may engage the child
restraint locking feature. If this happens, just let the
belt go back all the way and start again.
Engaging the child restraint locking feature may
affect the passenger sensing system. See
Passenger Sensing System on page 1-80.3. Push the latch plate into the buckle until it clicks.
Pull up on the latch plate to make sure it is secure.
If the belt is not long enough, seeSafety Belt
Extender on page 1-35.
Make sure the release button on the buckle is
positioned so you would be able to unbuckle the
safety belt quickly if necessary.
4. If equipped with a shoulder belt height adjuster,
move it to the height that is right for you. Improper
shoulder belt height adjustment could reduce
the effectiveness of the safety belt in a crash. See
“Shoulder Belt Height Adjustment” later in this
section.
1-28
Page 55 of 578

{CAUTION:
Children can be seriously injured or strangled
if a shoulder belt is wrapped around their neck
and the safety belt continues to tighten.
Secure any unused safety belts behind the
child restraint so children cannot reach them.
Pull the shoulder belt all the way out of the
retractor to set the lock, if your vehicle has
one, after the child restraint has been installed.
Be sure to follow the instructions of the child
restraint manufacturer.Notice:Contact between the child restraint LATCH
attachment parts and the vehicle’s safety belt
assembly may cause damage to these parts. Make
sure when securing unused safety belts behind
the child restraint that there is no contact between
the child restraint LATCH attachment parts and
the vehicle’s safety belt assembly.
Folding an empty rear seat with the safety belts
secured may cause damage to the safety belt or the
seat. When removing the child restraint, always
remember to return the safety belts to their normal,
stowed position before folding the rear seat.
1-51
Page 60 of 578
4. Pull the rest of the shoulder belt all the way out of
the retractor to set the lock.5. To tighten the belt, push down on the child restraint,
pull the shoulder portion of the belt to tighten the
lap portion of the belt, and feed the shoulder
belt back into the retractor. If you are using a
forward-facing child restraint, you may nd it helpful
to use your knee to push down on the child
restraint as you tighten the belt.
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Page 64 of 578
3. Pick up the latch plate, and run the lap and shoulder
portions of the vehicle’s safety belt through or
around the restraint. The child restraint instructions
will show you how.
4. Push the latch plate into the buckle until it clicks.
Make sure the release button is positioned so you
would be able to unbuckle the safety belt quickly
if necessary.5. Pull the rest of the shoulder belt all the way out of
the retractor to set the lock.
1-60
Page 68 of 578
5. Pull the rest of the shoulder belt all the way out of
the retractor to set the lock.6. To tighten the belt, push down on the child restraint,
pull the shoulder portion of the belt to tighten the
lap portion of the belt and feed the shoulder
belt back into the retractor. If you are using a
forward-facing child restraint, you may nd it helpful
to use your knee to push down on the child
restraint as you tighten the belt.
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Page 71 of 578
3. Pick up the latch plate, and run the lap and shoulder
portions of the vehicle’s safety belt through or
around the restraint. The child restraint instructions
will show you how.
4. Push the latch plate into the buckle until it clicks.
Make sure the release button is positioned so you
would be able to unbuckle the safety belt quickly
if necessary.5. Pull the rest of the shoulder belt all the way out of
the retractor to set the lock.
1-67
Page 87 of 578

Safety belts help keep the passenger in position on the
seat during vehicle maneuvers and braking, which
helps the passenger sensing system maintain the
passenger airbag status. See “Safety Belts” and “Child
Restraints” in the Index for additional information
about the importance of proper restraint use.If you ever pull the shoulder portion of the belt out all
the way, you will engage the child restraint locking
feature. This may unintentionally cause the passenger
sensing system to turn the airbag(s) off for some
adult size occupants. If this happens, just let the belt go
back all the way and start again.
{CAUTION:
If the airbag readiness light in the instrument
panel cluster ever comes on and stays on, it
means that something may be wrong with the
airbag system. If this ever happens, have the
vehicle serviced promptly, because an
adult-size person sitting in the right front
passenger’s seat may not have the protection
of the airbag(s). SeeAirbag Readiness Light
on page 3-38for more on this, including
important safety information.
1-83