2002 GMC YUKON XL coolant level

2-80Low Coolant This message is displayed
when the cooling system is
low on coolant.
The engine may overheat. See ªEngine Coolantº in
the Index and have your vehicle serviced as soon as
you can.
Check Coolant Temp This message is displayed
when the cooling system
temperature gets hot.
Check the coolant temperature gage and the coolant
level. See ªEngine Coolant,º ªEngine Coolant
Temperature Gageº and ªEngine Overheatingº in the
Index for further information. Engine Overheated This message is displayed
when the cooling system
temperature gets too hot.
This message will be displayed after the air conditioning
system has automatically turned off for the engine
coolant protection mode. See ªEngine Overheatingº in
the Index for further information.
Reduced Engine Power This message is displayed
when the cooling system
temperature gets too hot
and the engine further
enters the engine coolant
protection mode.
See ªEngine Overheatingº in the Index for
further information.

3-5Mode Knob
- Automatic Operation
When the system is set in AUTO mode, sensors will
control the air delivery mode. Air will come primarily
from the floor or instrument panel outlets, with some air
directed to the windshield to prevent fogging.
When the system is in AUTO mode, the air conditioning
light will turn on, and the recirculation and outside air
lights will turn off. With the system in full automatic
control (both the fan and mode knobs in AUTO), you
still have the ability to override any function. However,
continually overriding the outside air or the A/C
compressor will limit the ability of the system to cool
the vehicle quickly.
If you push a button for a function which is not
available, the light next to that button will flash three
times to alert you that it's not available.
To find your comfort zone, start with the 74
F (23
C)
setting and allow about 20 minutes for the system to
adjust the temperature if necessary. With the automatic setting, the air conditioning
compressor automatically cycles when needed to cool
the air. In cold weather, when the system senses the
need for heat, the airflow will be directed out the floor
outlets. As the interior temperature approaches a desired
setting, the fan speed will decrease. To maintain interior
comfort, the airflow will adjust between the instrument
panel outlets and floor outlets. On bright sunny days
in cool weather, the airflow may come out of the
instrument panel and the floor outlets (bi
- level mode)
to maintain comfort and prevent stuffiness.
To avoid blowing cold air in cold weather, the system
will delay turning on the fan until warm air is available.
The length of delay depends on the outside air
temperature, engine coolant temperature or the time
since the engine was last started. As the coolant
warms up, the fan speed will gradually increase and
air will flow from the floor outlets, with some airflow
to the windshield to prevent fogging under most
normal conditions.
Be careful not to put anything over the solar sensor
located near the center of the instrument panel.
This sensor is used by the automatic system to
regulate temperature.

3-8Air Conditioning On hot days, open the windows long enough to let hot
air inside escape. This reduces the time it takes for your
vehicle to cool down. Then keep your windows closed
for the air conditioner to work its best.
The A/C button, located below the mode knob, allows
the air coming into your vehicle to be cooled. This
setting is useful for normal cooling on hot days.
Use A/C with recirculation on to allow the air inside
your vehicle to be recirculated. This setting will help to
maximize your air conditioner's performance and your
vehicle's fuel economy. This setting also cools the air
the fastest and can be used to keep unwanted odors
and/or dust from entering the vehicle.
When using the air conditioner, turn off the recirculation
setting and use the outside air setting after the vehicle
reaches a comfortable interior temperature. When the
right knob on the control panel is between floor and
defrost, the recirculation feature will not function.
This helps reduce window fogging. Passenger Compartment Air Filter
Your vehicle is equipped with a passenger compartment
air filter which filters outside air entering the vehicle.
For information on replacing the filter see ªPassenger
Compartment Air Filterº in the Index.
Heating The heater works best if you keep your windows closed
while using it. On cold days, use the floor or bi
- level
(mode knob set between vent and floor) setting with the
temperature knob in the red area.
On cold days, approximately 32
F (
- 0
C) or lower,
you may experience differences in how the transmission
shifts until the engine is warm. This feature
automatically reduces the time it takes for the engine to
reach normal operating temperature and shortens the
time it takes the heater to reach full output.
If you use the engine coolant heater before starting your
engine in cold weather, 20
F (
- 8
C) or lower, the
heating system will produce warmer air faster to heat the
passenger compartment.
The use of an engine coolant heater also reduces the
time it takes for the engine to reach normal operating
temperature. For more information, see ªEngine Coolant
Heaterº in the Index.

4-53Driving 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 can tow in DRIVE (D). 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).
You may also want to activate the tow/haul mode if the
transmission shifts too often. See ªTow/Haul Modeº in
the Index.
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. 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 shift into PARK (P).
5. Release the regular brakes.

5-12Cooling System When you decide it's safe to lift the hood, here's what
you'll see:
A. Coolant Surge Tank
B. Coolant Surge Tank Pressure Cap
C. Engine Fan
If the coolant inside the coolant surge tank is boiling,
don't do anything else until it cools down. The vehicle
should be parked on a level surface. The coolant level should
be at or above the FILL
COLD mark. If it isn't,
you may have a leak at the
pressure cap or in the
radiator hoses, heater
hoses, radiator, water
pump or somewhere else
in the cooling system.
CAUTION: Heater and radiator hoses, and other engine
parts, can be very hot. Don't touch them. If you
do, you can be burned.
Don't run the engine if there is a leak. If you run
the engine, it could lose all coolant. That could
cause an engine fire, and you could be burned.
Get any leak fixed before you drive the vehicle.

5-14How to Add Coolant to the Coolant
Surge Tank If you haven't found a problem yet, check to see if
coolant is visible in the surge tank. If coolant is visible
but the coolant level isn't at or above the FILL COLD
mark, add a 50/50 mixture of clean, drinkable water and
DEX
- COOL

coolant at the coolant surge tank, but be
sure the cooling system, including the coolant surge tank
pressure cap, is cool before you do it. See ªEngine
Coolantº in the Index for more information.
If no coolant is visible in the surge tank, add coolant
as follows: CAUTION: Steam and scalding liquids from a hot cooling
system can blow out and burn you badly. They are
under pressure, and if you turn the coolant surge
tank pressure cap
-- even a little
-- they can come
out at high speed. Never turn the cap when the
cooling system, including the coolant surge tank
pressure cap, is hot. Wait for the cooling system
and coolant surge tank pressure cap to cool if you
ever have to turn the pressure cap.

5-16 The coolant surge tank on
your vehicle may be
equipped with one of the
two caps shown.
1. Park the vehicle on a level surface. You can remove
the coolant surge tank pressure cap when the cooling
system, including the coolant surge tank pressure cap
and upper radiator hose, is no longer hot. Turn the
pressure cap slowly counterclockwise (left) about
one full turn. If you hear a hiss, wait for that to stop.
A hiss means there is still some pressure left.

5-18 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 FILL COLD mark. 5. Then replace the pressure cap. Be sure the pressure
cap is hand
- tight and fully seated.