2004 GMC YUKON DENALI trailer

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 ¯uid (don't over®ll),
engine oil, axle lubricant, belts, cooling system and
brake system. Each of these is covered in this manual,
and the Index will help you ®nd 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.
4-61

Trailer Wiring Harness
Heavy-Duty Trailer Wiring Package
Your vehicle is equipped with the seven-wire trailer
towing harness. This harness with a seven-pin universal
heavy-duty trailer connector is attached to a bracket
on the hitch platform.The Center High-Mounted Stoplamp (CHMSL) wire is
tied next to the trailer wiring harness for use with a
trailer.
The seven-wire harness contains the following trailer
circuits:
·Yellow: Left Stop/Turn Signal
·Dark Green: Right Stop/Turn Signal
·Brown: Taillamps
·White: Ground
·Light Green: Back-up Lamps
·Red: Battery Feed
·Dark Blue: Trailer Brake
4-62

Instrument Panel Jumper Wiring Harness
{CAUTION:
Be sure to use only the correct trailer brake
harness, the one intended for use on your
vehicle. If you use some other trailer brake
harness, even if it seems to ®t, your trailer
brakes may not work at all. You could have a
crash in which you or others could be injured.
Use only the trailer brake harness intended for
your vehicle. If it is no longer available to you,
be sure to get a proper replacement from your
dealer.This harness is included with your vehicle as part of the
heavy-duty trailer wiring package.
This harness is for an electric brake controller and
includes a trailer battery feed fuse. It should be installed
by your dealer or a quali®ed service center.
4-63

Four-Wire Harness Adapter
This adapter is included
with your vehicle as part of
the heavy-duty trailer
wiring package.
Use this adapter to connect a standard four-way round
pin connector to the seven-wire harness on your
vehicle.Connect the adapter with the tab pointing up (see
arrow). The ¯ip cap on the vehicle's seven-wire harness
will lock onto the tab and help hold the adapter in
place. Plug the four-way round pin connector onto the
adapter.
4-64

Automatic Transmission Fluid
When to Check and Change
A good time to check your automatic transmission ¯uid
level is when the engine oil is changed.
Change both the ¯uid and ®lter every 50,000 miles
(83 000 km) if the vehicle's GVWR is over 8,600 or if
the vehicle is mainly driven under one or more of these
conditions:
·In heavy city traffic where the outside temperature
regularly reaches 90ÉF (32ÉC) or higher.
·In hilly or mountainous terrain.
·When doing frequent trailer towing.
·Uses such as found in taxi, police or delivery
service.
If your vehicle's GVWR is not over 8,600 and you do
not use your vehicle under any of these conditions,
change the ¯uid and ®lter every 100,000 miles
(166 000 km).
See
Scheduled Maintenance on page 6-4.
How to Check
Because this operation can be a little difficult, you may
choose to have this done at the dealership service
department.
If you do it yourself, be sure to follow all the instructions
here, or you could get a false reading on the dipstick.
Notice:Too much or too little ¯uid can damage
your transmission. Too much can mean that some
of the ¯uid could come out and fall on hot engine
part or exhaust system parts, starting a ®re.
Too little ¯uid could cause the transmission to
overheat. Be sure to get an accurate reading if you
check your transmission ¯uid.
Wait at least 30 minutes before checking the
transmission ¯uid level if you have been driving:
·When outside temperatures are above 90ÉF (32ÉC).
·At high speed for quite a while.
·In heavy traffic ± especially in hot weather.
·While pulling a trailer.
To get the right reading, the ¯uid should be at
normal operating temperature, which is 180ÉF to 200ÉF
(82ÉC to 93ÉC).
5-20

Adding Coolant
If you need more coolant, add the proper DEX-COOLž
coolant mixtureat the surge tank, but only when the
engine is cool.
{CAUTION:
You can be burned if you spill coolant on hot
engine parts. Coolant contains ethylene glycol,
and it will burn if the engine parts are hot
enough. Do not spill coolant on a hot engine.
When replacing the pressure cap, make sure it is
hand-tight.
Coolant Surge Tank Pressure Cap
The coolant surge tank pressure cap must be fully
installed on the coolant surge tank. SeeEngine
Compartment Overview on page 5-12for more
information on location.
Notice:If the pressure cap is not tightly installed,
coolant loss and possible engine damage may
occur. Be sure the cap is properly and tightly
secured.
Engine Overheating
You will ®nd a coolant temperature gage on your
vehicle's instrument panel. SeeEngine Coolant
Temperature Gage on page 3-38. In addition, you will
®nd an ENGINE COOLANT HOT, ENGINE
OVERHEATED and a REDUCED ENGINE POWER
message in the DIC on the instrument panel. See
DIC
Warnings and Messages on page 3-57.
Overheated Engine Protection
Operating Mode
If an overheated engine condition exists and the
REDUCED ENGINE POWER message is displayed, an
overheat protection mode which alternates ®ring
groups of cylinders helps prevent engine damage. In
this mode, you will notice a loss in power and engine
performance. This operating mode allows your vehicle to
be driven to a safe place in an emergency. Driving
extended miles (km) and/or towing a trailer in the
overheat protection mode should be avoided.
Notice:After driving in the overheated engine
protection operating mode, to avoid engine damage,
allow the engine to cool before attempting any
repair. The engine oil will be severely degraded.
Repair the cause of coolant loss, change the oil and
reset the oil life system. See
Engine Oil on
page 5-13.
5-25

If No Steam Is Coming From Your
Engine
An overheat warning, along with a low coolant condition,
can indicate a serious problem. For more information
see
Driver Information Center (DIC) on page 3-46.
If you get an engine overheat warning, and don't have a
low coolant condition, 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. SeeTowing a Trailer on page 4-51.
If you get the overheat warning with no sign of steam, try
this for a minute or so:
1. Turn on your heater to full hot at the highest fan
speed and open the window as necessary.
2. If you're in a traffic jam, shift to NEUTRAL (N);
otherwise, shift to the highest gear while
driving ± DRIVE (D).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 vehicleuntil it
cools down. Also, see ªOverheated Engine Protection
Operating Modeº listed previously in this section.
You may decide not to lift the hood but to get service
help right away.
5-27

4. With the coolant surge tank pressure cap off, start
the engine and let it run until you can feel the upper
radiator hose getting hot. Watch out for the
engine cooling fan.
By this time, the coolant level inside the coolant
surge tank may be lower. If the level is lower, add
more of the proper mixture to the coolant surge tank
until the level reaches FULL COLD mark.
5. Then replace the pressure cap. Be sure the
pressure cap is hand-tight and fully seated.
Engine Fan Noise
Your vehicle has a clutched engine cooling fan. When
the clutch is engaged, the fan spins faster to provide
more air to cool the engine. In most everyday driving
conditions, the fan is spinning slower and the clutch is
not fully engaged. This improves fuel economy and
reduces fan noise. Under heavy vehicle loading, trailer
towing and/or high outside temperatures, the fan
speed increases as the clutch more fully engages.
So you may hear an increase in fan noise. This
is normal and should not be mistaken as the
transmission slipping or making extra shifts. It is merely
the cooling system functioning properly. The fan will
slow down when additional cooling is not required and
the clutch disengages.
You may also hear this fan noise when you start the
engine. It will go away as the fan clutch partially
disengages.
5-33