2003 GMC YUKON DENALI brakes

Braking
Braking action involves perception time and
reaction time.
First, you have
to decide to push on the brake pedal.
That’s perception time. Then you have
to bring up your
foot and do it. That’s reaction time.
Average reaction time is about 314 of a second. But
that’s only an average.
It might be less with one driver
and as long as two or three seconds or more with
another. Age, physical condition, alertness, coordination
and eyesight all play a part.
So do alcohol, drugs and
frustration.
But even in 3/4 of a second, a vehicle moving
at 60 mph
(100 km/h) travels 66 feet (20 m). That
could be a
lot of distance in an emergency, so keeping
enough space between your vehicle and others is
important.
And, of course, actual stopping distances vary greatly
with the surface of the road (whether it’s pavement
or gravel); the condition of the road (wet, dry, icy); tire
tread; the condition of your brakes; the weight of
the vehicle and the amount of brake force applied. Avoid needless heavy
braking. Some people drive in
spurts
- heavy acceleration followed by heavy
braking
- rather than keeping pace with traffic. This is
a mistake. Your brakes may not have time
to cool
between hard stops. Your brakes will wear out much
faster
if you do a lot of heavy braking. If you keep pace
with the traffic and allow realistic following distances,
you will eliminate a
lot of unnecessary braking.
That means better braking and longer brake life.
If your engine ever stops while you’re driving, brake
normally but don’t pump your brakes.
If you do,
the pedal may get harder
to push down. If your engine
stops, you will still have some power brake assist.
But you will use it when you brake. Once the power
assist is used up, it may take longer
to stop and
the brake pedal will be harder
to push.
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Anti-lock Brake System
Your vehicle has anti-lock brakes. ABS is an advanced
electronic braking system that will help prevent a
braking skid.
When you start your engine and begin to drive away,
your anti-lock brake system will check itself. You
may hear a momentary motor or clicking noise while
this test is going on. This is normal.
If there’s a problem with
the anti-lock brake system, this warning light
will
stay on. See Anti-Lock
Brake System Warning
Light
on page 3-35.
Along with ABS, your vehicle has a Dynamic Rear
Proportioning (DRP) system.
If there’s a DRP problem,
both the brake and ABS warning lights will come
on
accompanied by a IO-second chime. The lights
and chime will come
on each time the ignition is turned
on until the problem is repaired. See your dealer for
service. Let’s say
the road is wet and you’re driving safely.
Suddenly, an animal jumps out in front of you. You slam
on the brakes and continue braking. Here’s what
happens with ABS:
A computer senses that wheels are slowing down. If
one of the wheels is about to stop rolling, the computer
will separately work the brakes at each front wheel
and at both rear wheels.
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When the Stabilitrak@system has been turned off you
may still hear system noises as a result of the
brake-traction control coming on.
It is recommended to leave the system on for normal
driving conditions, but it may be necessary
to turn
the system
off if your vehicle is stuck in sand, mud, ice
or snow, and you want
to “rock” your vehicle to
attempt to free it. It may also be necessary to turn off
the system when driving in extreme off-road conditions
where high wheel spin is required. See If
You Are
Stuck: In Sand, Mud, Ice or Snow on page
4-4 1.
Traction Control Operation
The traction control system is part of the
Stabilitrak@system. Traction control limits wheel spin by
reducing engine power
to the wheels (engine speed
management) and by applying brakes
to each individual
wheel (brake-traction control) as necessary.
The traction control system is enabled automatically
when you start your vehicle, and it will activate
and display the TRACTION ACTIVE message in the
Driver Information Center (DIC)
if it senses that any of
the wheels are spinning or beginning to lose traction
while driving. If you turn
off Stabilitrak@, only the
brake-traction control portion
of traction control will
work. The engine speed management will be disabled.
In this state, engine power is not reduced automatically
and the driven wheels can spin more freely. This
can cause the brake-traction control
to activate
constantly. For more information on the traction active
message, see Driver Information Center (DIC) on
page
3-43.
Notice: If the traction off light comes on due to
heavy braking and/or because the traction control
system has been continuously active, do not allow
the wheel@) of one axle to spin excessively.
If you
do, you may be causing damage to your transfer
case. This could lead to costly repairs not covered by
your warranty.
If the brake-traction control system activates constantly
or
if the brakes have heated up due to high speed
braking, the brake-traction control will be automatically
disabled. The system will come back on after the
brakes have cooled. This can take up
to two minutes ot
longer depending on brake usage.
Notice: Don’t allow the wheel(s) of one axle to spin
excessively when the traction
off, ABS and brake
lights are on and the
SERVICE STABILITY MESSAGE
is displayed. In this situation, damage to the transfer
case
is possible. This could lead to costly repairs not
covered by your warranty. You should immediately
reduce engine power until the lights and messages
are no longer displayed.
4-1 0

Speed limit signs near curves warn that you should
adjust your speed. Of course, the posted speeds
are based on good weather and road conditions. Under
less favorable conditions you’ll want to go slower.
If you need to reduce your speed as you approach a
curve, do it before you enter the curve, while your front
wheels are straight ahead.
Try
to adjust your speed so you can “drive” through the
curve. Maintain a reasonable, steady speed. Wait to
accelerate until you are out of the curve, and then
accelerate gently into the straightaway.
Steering in Emergencies
There are times when steering can be more effective
than braking. For example, you come over a hill and find
a truck stopped in your lane, or a car suddenly pulls
out from nowhere, or a child darts out from between
parked cars and stops right in front
of you. You
can avoid these problems by braking
- if you can stop
in time. But sometimes you can’t; there isn’t room.
That’s the time for evasive action
- steering around the
problem.
Your vehicle can perform very well in emergencies like
these. First apply your brakes.
See
Braking on page 4-6. It is better to remove as much
speed as you can from a possible collision. Then
steer around the problem, to the left or right depending
on the space available.
4-1
2
An emergency like this requires close attention and a
quick decision. If you are holding the steering wheel at
the recommended
9 and 3 o’clock positions, you
can turn it a full
180 degrees very quickly without
removing either hand. But you have to act fast, steer
quickly, and just as quickly straighten the wheel
once you have avoided the object.
The fact that such emergency situations are always
possible is a good reason
to practice defensive driving
at all times and wear safety belts properly.

Loss of Control
Let’s review what driving experts say about what happens
when the three control systems (brakes, steering and
acceleration) don’t have enough friction where the tires
meet the road
to do what the driver has asked.
In any emergency, don’t give up. Keep trying
to steer
and constantly seek an escape route or area of
less danger.
In a skid, a driver can lose control of the vehicle.
Defensive drivers avoid most skids by taking reasonable
care suited to existing conditions, and by not
“overdriving” those conditions. But skids are always
possible.
The three types of skids correspond
to your vehicle’s
three control systems. In the braking skid, your wheels
aren’t rolling. In the steering or cornering skid,
too much
speed or steering in a curve causes tires to slip and lose
cornering force. And in the acceleration skid,
too much
throttle causes the driving wheels
to spin.
A cornering skid is best handled by easing your foot off
the accelerator pedal.
If your vehicle starts to slide, ease your foot off the
accelerator pedal and quickly steer the way you want
the vehicle
to go. If you start steering quickly enough,
your vehicle may straighten out. Always be ready
for
a second skid if it occurs.
Of course, traction is reduced when water, snow, ice,
gravel or other material is on the road. For safety, you’ll
want
to slow down and adjust your driving to these
conditions.
It is important to slow down on slippery
surfaces because stopping distance will be longer and
vehicle control more limited.
While driving on a surface with reduced traction, try
your best
to avoid sudden steering, acceleration
or braking (including engine braking by shifting
to a
lower gear). Any sudden changes could cause the tires
to slide. You may not realize the surface is slippery
until your vehicle is skidding. Learn
to recognize warning
clues
- such as enough water, ice or packed snow
on the road
to make a “mirrored surface” - and slow
down when you have any doubt.
Remember: Any anti-lock brake system (ABS) helps
avoid only the braking skid.
4-1 5

Driving Downhill
When off-roading takes you downhill, you’ll want to
consider a number of things:
How steep is the downhill? Will I be able to maintain
vehicle control?
0 What’s the surface like? Smooth? Rough? Slippery?
Hard-packed dirt? Gravel?
Are there hidden surface obstacles? Ruts? Logs?
Boulders?
What’s at the bottom of the hill? Is there a hidden
creek bank or even a river bottom with large rocks?
If you decide you can go down a hill safely, then try to
keep your vehicle headed straight down, and use a
low gear. This way, engine drag can help your brakes
and they won’t have to do all the work. Descend slowly,
keeping your vehicle under control at all times.
Heavy braking when going down a hill can
cause your brakes to overheat and fade.
This could cause
loss of control and a serious
accident. Apply the brakes lightly when
descending a hill and use a
low gear to keep
vehicle speed under control.
0: Are there some things I should not do when
driving down a hill?
A: Yes! These are important because if you ignore
them you could lose control and have a serious
accident.
When driving downhill, avoid turns that take you
across the incline of the hill. A hill that’s not too
steep to drive down may be too steep to drive across. You could roll over
if you don’t drive
straight down.
Never go downhill with the transmission in
NEUTRAL (N). This is called “free-wheeling.”
Your brakes will have to
do all the work and could
overheat and fade.
4-23

Q: Am I likely to stall when going downhill?
A: It’s much more likely to happen going uphill. But if it
happens going downhill, here’s what
to do.
Stop your vehicle by applying the regular brakes.
Apply the parking brake.
Shift to PARK (P) and, while still braking, restart the
Shift back to a low gear, release the parking brake,
If the engine won’t start, get out and get help.
engine.
and
drive straight down.
Driving Across an Incline
Sooner or later, an off-road trail will probably go across
the incline
of a hill. If this happens, you have to
decide whether
to try to drive across the incline. Here
are some things
to consider:
A hill that can be driven straight up or down may be
too steep to drive across. When you go straight up
or down a
hill, the length of the wheel base (the
distance from the front wheels
to the rear wheels)
reduces the likelihood the vehicle will tumble end
over end. But when you drive across an incline,
the much more narrow track width (the distance
between the left and right wheels) may not prevent
the vehicle from tilting and rolling over.
Also,
driving across an incline puts more weight on the
downhill wheels. This could cause a downhill
slide or a rollover.
Surface conditions can be a problem when you
drive across a hill.
Loose gravel, muddy spots,
or even wet grass can cause your tires
to slip
sideways, downhill.
If the vehicle slips sideways,
it can hit something that will trip
it (a rock, a rut, etc.)
and roll over.
Hidden obstacles can make the steepness of the
incline even worse. If you drive across a rock
with the uphill wheels, or
if the downhill wheels
drop into a rut or depression, your vehicle can tilt
even more.
For reasons like these, you need to decide carefully
whether to try to drive across an incline. Just because
the trail goes across the incline doesn’t mean you
have to drive it. The last vehicle to try it might have
rolled over.
4-24

Driving in Water
Heavy rain can mean flash flooding, and flood waters
demand extreme caution.
Find out how deep the water
is before you drive through
it. If it’s deep enough to cover your wheel hubs, axles
or exhaust pipe, don’t try
it - you probably won’t
get through. Also, water that deep can damage your
axle and other vehicle parts.
If the water isn’t too deep, drive slowly through it. At
faster speeds, water splashes on your ignition system
and your vehicle can stall. Stalling can also occur
if you
get your tailpipe under water. And, as long as your
tailpipe is under water, you’ll never be able to start your
engine. When you go through water, remember that
when your brakes get wet, it may take you longer
to stop.
I
- - - - -ng through rushing water can be
dangerous. Deep water can sweep your vehicle
downstream and you and your passengers
i could drown. If it’s only shallow water, it can
still wash away the ground from under your
tires, and you could lose traction and roll the
vehicle over. Don’t drive through rushing water.
I I
See Driving in Rain and on Wet Roads on page 4-29 for
more information on driving through water.
After Off-Road Driving
Remove any brush or debris that has collected on the
underbody, chassis or under the hood. These
accumulations can be a fire hazard.
After operation in mud or sand, have the brake linings
cleaned and checked. These substances can cause
glazing and uneven braking. Check the body structure,
steering, suspension, wheels, tires and exhaust
system for damage.
Also, check the fuel lines and
cooling system for any leakage.
Your vehicle will require more frequent service due to
off-road use. Refer
to the Maintenance Schedule
for additional information.
4-27