engine GMC YUKON 1999 Workshop Manual

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4-49 Trailer Brakes
If your trailer weighs more than 1,000 lbs. (450 kg)
loaded, then it needs its own brakes
-- and they must be
adequate. Be sure to read and follow the instructions for
the trailer brakes so you'll be able to install, adjust and
maintain them properly.
Your trailer brake system can tap into the vehicle's
hydraulic brake system only if:

The trailer parts can withstand 3,000 psi
(20 650 kPa) of pressure.

The trailer's brake system will use less than
0.02 cubic inch (0.3 cc) of fluid from your vehicle's
master cylinder. Otherwise, both braking systems
won't work well. You could even lose your brakes.
If everything checks out this far, make the brake tap at
the port on the master cylinder that sends the fluid to the
rear brakes. But don't use copper tubing for this. If
you do, it will bend and finally break off. Use steel
brake tubing.
Driving with a Trailer
CAUTION:
If you have a rear-most window open and you
pull a trailer with your vehicle, carbon monoxide
(CO) could come into your vehicle. You can't see
or smell CO. It can cause unconsciousness or
death. (See ªEngine Exhaustº in the Index.) To
maximize your safety when towing a trailer:

Have your exhaust system inspected for
leaks, and make necessary repairs before
starting on your trip.

Keep the rear
-most windows closed.

If exhaust does come into your vehicle
through a window in the rear or another
opening, drive with your front, main
heating or cooling system on and with the
fan on any speed. This will bring fresh,
outside air into your vehicle. Do not use the
recirculation button or MAX because it
only recirculates the air inside your vehicle.
(See ªComfort Controlsº in the Index.)

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4-51 Making Turns
NOTICE:
Making very sharp turns while trailering could
cause the trailer to come in contact with the
vehicle. Your vehicle could be damaged. Avoid
making very sharp turns while trailering.
When you're turning with a trailer, make wider turns
than normal. Do this so your trailer won't strike soft
shoulders, curbs, road signs, trees or other objects.
Avoid jerky or sudden maneuvers. Signal well
in advance.
Turn Signals When Towing a Trailer
The arrows on your instrument panel will flash
whenever you signal a turn or lane change. Properly
hooked up, the trailer lamps will also flash, telling other
drivers you're about to turn, change lanes or stop.
When towing a trailer, the arrows on your instrument
panel will flash for turns even if the bulbs on the trailer
are burned out. Thus, you may think drivers behind youare seeing your signal when they are not. It's important
to check occasionally to be sure the trailer bulbs are
still working.
Driving On Grades
Reduce speed and shift to a lower gear before you start
down a long or steep downgrade. If you don't shift
down, you might have to use your brakes so much that
they would get hot and no longer work well.
You should tow in AUTOMATIC OVERDRIVE (
).
You may want to shift the transmission to THIRD (3) or,
if necessary, a lower gear selection if the transmission
shifts too often (e.g., under heavy loads and/or
hilly conditions).
When towing at high altitude on steep uphill grades,
consider the following: Engine coolant will boil at a lower
temperature than at normal altitudes. If you turn your
engine off immediately after towing at high altitude on
steep uphill grades, your vehicle may show signs similar to
engine overheating. To avoid this, let the engine run while
parked (preferably on level ground) with the automatic
transmission in PARK (P) for a few minutes before turning
the engine off. If you do get the overheat warning, see
ªEngine Overheatingº in the Index.

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4-52 Parking on Hills
CAUTION:
You really should not park your vehicle, with a
trailer attached, on a hill. If something goes
wrong, your rig could start to move. People can
be injured, and both your vehicle and the trailer
can be damaged.
But if you ever have to park your rig on a hill, here's
how to do it:
1. Apply your regular brakes, but don't shift into
PARK (P) yet.
2. Have someone place chocks under the trailer wheels.
3. When the wheel chocks are in place, release the
regular brakes until the chocks absorb the load.
4. Reapply the regular brakes. Then apply your parking
brake, and then shift to PARK (P).5. Be sure the transfer case is in a drive gear
-- not in
NEUTRAL (N).
6. Release the regular brakes.
CAUTION:
It can be dangerous to get out of your vehicle if
the shift lever is not fully in PARK (P) with the
parking brake firmly set. Your vehicle can roll.
If you have left the engine running, the vehicle
can move suddenly. You or others could be
injured. To be sure your vehicle won't move, even
when you're on fairly level ground, use the steps
that follow.
If you have four-wheel drive and your transfer
case is in NEUTRAL (N), your vehicle will be free
to roll, even if your shift lever is in PARK (P). So,
be sure the transfer case is in a drive gear
-- not
in NEUTRAL (N).

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4-53 When You Are Ready to Leave After
Parking on a Hill
1. Apply your regular brakes and hold the pedal down
while you:

Start your engine;

Shift into a gear; and

Release the parking brake.
2. Let up on the brake pedal.
3. Drive slowly until the trailer is clear of the chocks.
4. Stop and have someone pick up and store the chocks.
Maintenance When Trailer Towing
Your vehicle will need service more often when you're
pulling a trailer. See the Maintenance Schedule for more
on this. Things that are especially important in trailer
operation are automatic transmission fluid (don't
overfill), engine oil, axle lubricant, belt, cooling system
and brake adjustment. Each of these is covered in this
manual, and the Index will help you find them quickly.
If you're trailering, it's a good idea to review these
sections before you start your trip.
Check periodically to see that all hitch nuts and bolts
are tight.
Trailer Wiring Harness
Light-Duty Wiring Harness

5-
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5-1
Section 5 Problems On The Road
Here you'll find what to do about some problems that can occur on the road.
5
-2 Hazard Warning Flashers
5
-2 Other Warning Devices
5
-3 Jump Starting
5
-8 Towing Your Vehicle
5
-9 Engine Overheating5
-11 Cooling System
5
-18 Engine Fan Noise
5
-18 If a Tire Goes Flat
5
-19 Changing a Flat Tire
5
-32 If You're Stuck: In Sand, Mud, Ice or Snow

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5-5
4. Open the hoods and locate the batteries. Find the
positive (+) and negative (
-) terminals on
each battery.
CAUTION:
Using a match near a battery can cause battery
gas to explode. People have been hurt doing this,
and some have been blinded. Use a flashlight if
you need more light.
Be sure the battery has enough water. You don't
need to add water to the ACDelco Freedom

battery installed in every new GM vehicle. But if
a battery has filler caps, be sure the right amount
of fluid is there. If it is low, add water to take care
of that first. If you don't, explosive gas could
be present.
Battery fluid contains acid that can burn you.
Don't get it on you. If you accidentally get it in
your eyes or on your skin, flush the place with
water and get medical help immediately.
5. Check that the jumper cables don't have loose or
missing insulation. If they do, you could get a shock.
The vehicles could be damaged, too.
Before you connect the cables, here are some basic
things you should know. Positive (+) will go to
positive (+) and negative (
-) will go to a heavy
unpainted metal engine part. Don't connect
positive (+) to negative (
-) or you'll get a short
that would damage the battery and maybe other
parts, too.
CAUTION:
Fans or other moving engine parts can injure you
badly. Keep your hands away from moving parts
once the engine is running.

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5-7
dead battery. It goes to a heavy unpainted metal engine
part of the vehicle with the dead battery.
9. Attach the cable at least 18 inches (45 cm) away
from the dead battery, but not near engine parts that
move. The electrical connection is just as good
there, but the chance of sparks getting back to the
battery is much less.
10. Now start the vehicle with the good battery and run
the engine for a while.11. Try to start the vehicle with the dead battery.
If it won't start after a few tries, it probably
needs service.
12. Remove the cables in reverse order to prevent
electrical shorting. Take care that they don't touch
each other or any other metal.
A. Heavy Metal Engine Part
B. Good Battery
C. Dead Battery

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5-9
Engine Overheating
You will find a coolant temperature gage on your
vehicle's instrument panel. See ªEngine Coolant
Temperature Gageº in the Index.
If Steam Is Coming From Your Engine
CAUTION:
Steam from an overheated engine can burn you
badly, even if you just open the hood. Stay away
from the engine if you see or hear steam coming
from it. Just turn it off and get everyone away
from the vehicle until it cools down. Wait until
there is no sign of steam or coolant before you
open the hood.
If you keep driving when your engine is
overheated, the liquids in it can catch fire. You or
others could be badly burned. Stop your engine if
it overheats, and get out of the vehicle until the
engine is cool.
NOTICE:
If your engine catches fire because you keep
driving with no coolant, your vehicle can be
badly damaged. The costly repairs would not be
covered by your warranty.

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5-10 If No Steam Is Coming From Your Engine
If you get an engine overheat warning but see or hear no
steam, the problem may not be too serious. Sometimes
the engine can get a little too hot when you:

Climb a long hill on a hot day.

Stop after high
-speed driving.

Idle for long periods in traffic.

Tow a trailer. See ªDriving on Gradesº in the Index.
If you get the overheat warning with no sign of steam,
try this for a minute or so:
1. If your air conditioner is on, turn it off.
2. Turn on your heater to full hot at the highest fan
speed and open the window as necessary.
3. If you're in a traffic jam, shift to NEUTRAL (N);
otherwise, shift to the highest gear while
driving
-- AUTOMATIC OVERDRIVE (
).If you no longer have the overheat warning, you can
drive. Just to be safe, drive slower for about 10 minutes.
If the warning doesn't come back on, you can
drive normally.
If the warning continues, pull over, stop, and park your
vehicle right away.
If there's still no sign of steam, push down the
accelerator until the engine speed is about twice as fast
as normal idle speed for at least three minutes while
you're parked. If you still have the warning, turn off the
engine and get everyone out of the vehicle until it
cools down.
You may decide not to lift the hood but to get service
help right away.

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5-11
Cooling System
When you decide it's safe to lift the hood, here's what
you'll see:
A. Coolant Recovery Tank
B. Radiator Pressure Cap
C. Engine Fan
If the coolant inside the coolant recovery tank is boiling,
don't do anything else until it cools down.
The coolant level should be at or above the COLD mark.
If it isn't, you may have a leak in the radiator hoses,
heater hoses, radiator, water pump or somewhere else in
the cooling system.