2012 GMC SIERRA 1500 warning

Black plate (27,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Vehicle Care 10-27
Brakes
This vehicle has front disc brakes
and could have rear drum brakes or
rear disc brakes.
Disc brake pads have built-in wear
indicators that make a high-pitched
warning sound when the brake pads
are worn and new pads are needed.
The sound can come and go or be
heard all the time the vehicle is
moving, except when applying the
brake pedal firmly.
{WARNING
The brake wear warning sound
means that soon the brakes will
not work well. That could lead to
a crash. When the brake wear
warning sound is heard, have the
vehicle serviced.
Notice: Continuing to drive with
worn-out brake pads could result
in costly brake repair. Some driving conditions or climates
can cause a brake squeal when the
brakes are first applied or lightly
applied. This does not mean
something is wrong with the brakes.
Properly torqued wheel nuts are
necessary to help prevent brake
pulsation. When tires are rotated,
inspect brake pads for wear and
evenly tighten wheel nuts in the
proper sequence to torque
specifications in
Capacities and
Specifications on page 12‑2.
If the vehicle has rear drum brakes,
they do not have wear indicators,
but if a rear brake rubbing noise is
heard, have the rear brake linings
inspected immediately. Rear brake
drums should be removed and
inspected each time the tires are
removed for rotation or changing.
Drum brakes have an inspection
hole to inspect lining wear during
scheduled maintenance. When the
front brake pads are replaced, have
the rear brakes inspected, too. Brake linings should always be
replaced as complete axle sets.
Brake Pedal Travel
See your dealer if the brake pedal
does not return to normal height,
or if there is a rapid increase in
pedal travel. This could be a sign
that brake service might be
required.
Brake Adjustment
Every time the brakes are applied,
with or without the vehicle moving,
the brakes adjust for wear.
Replacing Brake System Parts
The braking system on a vehicle is
complex. Its many parts have to be
of top quality and work well together
if the vehicle is to have really good
braking. The vehicle was designed
and tested with top-quality brake
parts. When parts of the braking
system are replaced, be sure to get
new, approved replacement parts.

Black plate (28,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
10-28 Vehicle Care
If this is not done, the brakes might
not work properly. For example,
installing disc brake pads that are
wrong for the vehicle, can change
the balance between the front and
rear brakes—for the worse. The
braking performance expected can
change in many other ways if the
wrong replacement brake parts are
installed.
Brake Fluid
The brake master cylinder reservoir
is filled with DOT 3 brake fluid. See
Engine Compartment Overview on
page 10‑6 for the location of the
reservoir. There are only two reasons why the
brake fluid level in the reservoir
might go down:
.The brake fluid level goes down
because of normal brake lining
wear. When new linings are
installed, the fluid level goes
back up.
.A fluid leak in the brake
hydraulic system can also cause
a low fluid level. Have the brake
hydraulic system fixed, since a
leak means that sooner or later
the brakes will not work well.
Do not top off the brake fluid.
Adding fluid does not correct a leak.
If fluid is added when the linings
are worn, there will be too much
fluid when new brake linings are
installed. Add or remove brake fluid,
as necessary, only when work is
done on the brake hydraulic system.
{WARNING
If too much brake fluid is added, it
can spill on the engine and burn,
if the engine is hot enough. You
or others could be burned, and
the vehicle could be damaged.
Add brake fluid only when work
is done on the brake hydraulic
system. See “Checking Brake
Fluid” in this section.
When the brake fluid falls to a low
level, the brake warning light comes
on. See Brake System Warning
Light on page 5‑25.
Refer to the Maintenance Schedule
to determine when to check the
brake fluid. See Maintenance
Schedule on page 11‑3.

Black plate (29,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Vehicle Care 10-29
Checking Brake Fluid
Check brake fluid by looking at the
brake fluid reservoir. SeeEngine
Compartment Overview on
page 10‑6.
The fluid level should be above
MIN. If it is not, have the brake
hydraulic system checked to see if
there is a leak. After work is done on the brake
hydraulic system, make sure the
level is above the MIN but not over
the MAX mark.
What to Add
Use only new DOT 3 brake fluid
from a sealed container. See
Recommended Fluids and
Lubricants on page 11‑12.
Always clean the brake fluid
reservoir cap and the area around
the cap before removing it. This
helps keep dirt from entering the
reservoir.
{WARNING
With the wrong kind of fluid in
the brake hydraulic system, the
brakes might not work well. This
could cause a crash. Always use
the proper brake fluid.Notice
.Using the wrong fluid
can badly damage brake
hydraulic system parts. For
example, just a few drops of
mineral-based oil, such as
engine oil, in the brake
hydraulic system can
damage brake hydraulic
system parts so badly that
they will have to be replaced.
Do not let someone put in
the wrong kind of fluid.
.If brake fluid is spilled on the
vehicle's painted surfaces,
the paint finish can be
damaged. Be careful not
to spill brake fluid on the
vehicle. If you do, wash it off
immediately.

Black plate (30,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
10-30 Vehicle Care
Battery
If the vehicle is a Hybrid, see the
Hybrid Supplement for more
information.
This vehicle has a maintenance free
battery (or batteries). Refer to the
replacement number on the original
battery label when a new battery is
needed. SeeEngine Compartment
Overview on page 10‑6 for battery
location.
{WARNING
Battery posts, terminals, and
related accessories contain lead
and lead compounds, chemicals
known to the State of California to
cause cancer and reproductive
harm. Wash hands after handling.
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 on
page 10‑88 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.
Four-Wheel Drive
Transfer Case
When to Check Lubricant
Refer to Maintenance Schedule on
page 11‑3 to determine when to
check the lubricant.
How to Check Lubricant
Electric Shift Transfer Case
A. Fill Plug
B. Drain Plug

Black plate (35,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Vehicle Care 10-35
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. Firmly apply both the parking brake and the regular brake.
See Parking Brake on
page 9‑54.
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. Firmly apply the parking brake. See Parking Brake on
page 9‑54.
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
While parked, and with the parking
brake set, try to turn the ignition to
LOCK/OFF in each shift lever
position.
.The ignition should turn to
LOCK/OFF only when the shift
lever is in P (Park).
.The ignition key should come
out only in LOCK/OFF.
Contact your dealer if service is
required.

Black plate (36,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
10-36 Vehicle Care
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.
.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
inspected for wear or cracking.
See Maintenance Schedule on
page 11‑3 for more information on
wiper blade inspection.
Replacement blades come in
different types and are removed in
different ways. To remove the wiper
blade:
1. Pull the windshield wiper arm connector away from the
windshield.
2. Squeeze the grooved areas on
each side of the blade, and turn
the blade assembly away from
the arm connector.

Black plate (39,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
Vehicle Care 10-39
8. Turn the vertical aiming screwuntil the headlamp beam is
aimed to the horizontal tape
line. Turn it clockwise or
counterclockwise to raise or
lower the angle of the beam.
9. Make sure that the light from theheadlamp is positioned at the
bottom edge of the horizontal
tape line. The lamp on the
left (A) shows the correct
headlamp aim. The lamp on the
right (B) shows the incorrect
headlamp aim.
10. Repeat Steps 7 through 9 for the opposite headlamp.
Bulb Replacement
For the proper type of replacement
bulbs, see Replacement Bulbs on
page 10‑43.
For any bulb‐changing procedure
not listed in this section, contact
your dealer.
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.
Headlamps, Front Turn
Signal, Sidemarker, and
Parking Lamps
A. Side Marker Lamp
B. Low-Beam Headlamp
C. High-Beam Headlamp
D. Park/Turn Signal Lamp
1. Open the hood. See Hood on
page 10‑5
2. When replacing a driver side bulb on a vehicle with duel
batteries, see your dealer.

Black plate (50,1)GMC Sierra Owner Manual - 2012 - CRC - 11/15/11
10-50 Vehicle Care
Top View
Harness
Connector Usage
BODY 2 Body Harness
Connector 2
BODY 1 Body Harness
Connector 1
BODY 3 Body Harness
Connector 3
HEADLINER 3 Headliner
Harness
Connector 3 Harness
Connector Usage
HEADLINER 2 Headliner
Harness
Connector 2
HEADLINER 1 Headliner
Harness
Connector 1
SEO/
UPFITTER Special
Equipment Option
Upfitter Harness
Connector
Circuit
Breaker Usage
CB1 Passenger Side
Power Window Circuit
Breaker
CB2 Passenger Seat
Circuit Breaker
CB3 Driver Seat Circuit
Breaker
CB4 Rear Sliding Window
Wheels and Tires
Tires
Every new GM vehicle has
high-quality tires made by a
leading tire manufacturer.
See the warranty manual for
information regarding the tire
warranty and where to get
service. For additional
information refer to the tire
manufacturer.
{WARNING
.Poorly maintained and
improperly used tires are
dangerous.
.Overloading the tires can
cause overheating as a result
of too much flexing. There
could be a blowout and a
serious crash. See Vehicle
Load Limits on page 9‑16.
(Continued)