
Voltmeter Gage
When your engine is
running, the voltmeter
gage shows the charging
system voltage.
Readings in either warning zone indicate a possible
problem in the electrical system.
Readings in the low warning zone may occur when a
large number of electrical accessories are operating in
the vehicle and the engine is left at an idle for an
extended period. This condition is normal since the
charging system may not be able to provide full power
at engine idle. As engine speeds are increased, this
condition should correct itself because higher engine
speeds allow the charging system to create maximum
power.
You can only drive a short time on the battery. Be sure
to shut off the radio, the fan or any unnecessary
accessories and have the system serviced.
Service Transmission Warning Light
If your vehicle has an Allison®automatic transmission,
certain transmission malfunctions will turn this light on.
This light is located with
the auxiliary warning lights
in the center of the
instrument panel.
If this light comes on while you are driving, do not use
the transmission shift control or you may lose forward
gears. The computer for the transmission senses
a problem and chooses a gear to stay in so that you
can drive the vehicle in that gear. You may not be able
to drive as fast or back up when this light is on.
Notice:If you continue driving your vehicle after the
transmission warning light comes on, you could
damage the transmission. While this light is on, the
transmission cannot operate in all gears. If you
attempt to shift gears, the vehicle may not continue
to move. Do not attempt to shift gears while the
transmission warning light is on. Instead, drive
directly to an authorized dealer for service. If you
cannot drive to a dealer immediately, have the
vehicle towed.
3-31

Range Inhibit Warning Indicator
If your vehicle has an Allison 1000/2200/2300/2500 series
automatic transmission, a lighted bar under the current
gear selected will flash.
If your vehicle has an Allison 3000/3500 series
automatic transmission, the current gear selected on
the pushbutton display will flash.
The flashing bar or gear selection indicates that
transmission range shifts may not occur.
For detailed information on shift inhibit limitations, see
the Allison Automatic Transmission Operator’s Manual in
your vehicle for further information.
Brake System Warning Light
Your vehicle has either hydraulic or air brakes.
Each system has different warning lights.
Hydraulic Brake System Warning Lights
Vehicles with hydraulic brake systems have two brake
system warning lights on the instrument panel.
If the brake warning light
comes on, it means that
the fluid level in the master
cylinder reservoir is low or
there is another problem
with your hydraulic brakes.
When it comes on, you will also hear a warning tone.
This light should come on briefly when you turn the
ignition key to RUN. If it does not come on, then have it
fixed so it will be ready to warn you if there is a problem.
The brake warning light may come on, and the warning
tone may sound, when you are turning and braking
at the same time. This is normal. See “Hydraulic Brake
Systems” underBraking on page 4-4.
3-32

Engine Overspeed Warning Light
If your vehicle has this
light, it will come on if your
engine is operating at
too many revolutions per
minute (rpm).
It will also come on for a moment as a check when you
start your engine.
If it comes on when you’re driving, reduce your engine
speed immediately.
Engine Shutdown Warning Light
If your vehicle has the
engine shutdown feature,
this light will come on
when engine shutdown
is active.
SeeEngine Alarm and Automatic Shutdown on
page 2-18for more information.
Transmission Temperature Gage
If you have an automatic
transmission and this
gage, it is located
above the switchbank
in the center of the
instrument panel.
When your ignition is on, the gage shows the
temperature of the transmission oil. A reading in the
warning zone, the red area beginning at 300°F (150°C),
means you must stop driving and check into the cause.
One possible cause is a low oil level in the transmission.
Notice:If you drive your vehicle with the
transmission temperature gage above normal
operating range, you can damage the transmission.
This could lead to costly repairs that would not
be covered by your warranty. Do not drive your
vehicle while the transmission temperature gage
reading is above normal. See your dealer for service.
3-39

Traction Control System (TCS)
Your vehicle may have a traction control system that
limits wheel spin. This is especially useful in slippery road
conditions. The system operates only if it senses that one
or both of the rear wheels are spinning or beginning to
lose traction. When this happens, the system applies the
brake(s) at the affected wheel(s).
The bottom light on the TCS on/off button will come on
when the TCS is limiting wheel spin. You may feel
or hear the system working, but this is normal. The TCS
will function at speeds up to about 25 mph (42 km/h).
The TCS may operate on dry roads under some
conditions. When this happens, you may notice a
reduction in acceleration. This is normal and doesn’t
mean there’s a problem with your vehicle. Examples of
these conditions include a hard acceleration in a
turn, an abrupt upshift or downshift of the transmission
or driving on rough roads.
When the light in the top of the TCS button is on, the
TCS is off and will not limit wheel spin. Adjust your
driving accordingly.
The light in the top of the TCS button will come on if the
TCS is turned off by pressing the TCS on/off button.
The light may also come on if a problem has been
detected in either the traction control system or
the anti-lock brake system.The traction control system automatically comes on
whenever you start your vehicle. To limit wheel spin,
especially in slippery road conditions, you should always
leave the system on. But you can turn the traction control
system off if you ever need to. You should turn the
system off if your vehicle ever gets stuck in sand, mud or
snow and rocking the vehicle is required. SeeRocking
Your Vehicle to Get It Out on page 4-20for more
information.
To turn the system on or
off, press the traction
control button located on
the instrument panel.
If you used the TCS button to turn the system off, the
light in the top of the button will come on and stay
on. You can turn the TCS back on at any time by
pressing the button again; the light should go off.
4-8

Highway Hypnosis
Always be alert and pay attention to your surroundings
while driving. If you become tired or sleepy, find a
safe place to park your vehicle and rest.
Other driving tips include:
•Keep the vehicle well ventilated.
•Keep interior temperature cool.
•Keep your eyes moving — scan the road ahead
and to the sides.
•Check the rearview mirror and vehicle instruments
often.
Hill and Mountain Roads
Driving on steep hills or through mountains is different
than driving on flat or rolling terrain. Tips for driving
in these conditions include:
•Keep your vehicle serviced and in good shape.
•Check all fluid levels and brakes, tires, cooling
system, and transmission.
•Going down steep or long hills, shift to a
lower gear.
{CAUTION:
If you do not shift down, the brakes could get
so hot that they would not work well. You
would then have poor braking or even none
going down a hill. You could crash. Shift down
to let the engine assist the brakes on a steep
downhill slope.
{CAUTION:
Coasting downhill in NEUTRAL (N) or with the
ignition off is dangerous. The brakes will have
to do all the work of slowing down and they
could get so hot that they would not work well.
You would then have poor braking or even
none going down a hill. You could crash.
Always have the engine running and your
vehicle in gear when you go downhill.
4-15

Rocking Your Vehicle to Get It Out
First, turn the steering wheel left and right to clear
the area around the front wheels. For four-wheel-drive
vehicles, shift into 4HI. SeeFour-Wheel Drive on
page 2-32. Turn off any traction system. SeeTraction
Control System (TCS) on page 4-8. Then shift back and
forth between REVERSE (R) and a forward gear, or
with a manual transmission, between FIRST (1)
or SECOND (2) and REVERSE (R), spinning the wheels
as little as possible. To prevent transmission wear,
wait until the wheels stop spinning before shifting gears.
Release the accelerator pedal while you shift, and
press lightly on the accelerator pedal when the
transmission is in gear. By slowly spinning the wheels in
the forward and reverse directions, you will cause a
rocking motion that could free your vehicle. If that does
not get your vehicle out after a few tries, it might
need to be towed out. If your vehicle does need to be
towed out, seeTowing Your Vehicle on page 4-24.
Tow Hooks
{CAUTION:
These hooks, when used, are under a lot of
force. Always pull the vehicle straight out.
Never pull on the hooks at a sideways angle.
The hooks could break off and you or others
could be injured from the chain or cable
snapping back.
Notice:Never use tow hooks to tow the vehicle.
Your vehicle could be damaged and it would not be
covered by warranty.
4-20

Service............................................................5-4
Accessories and Modifications..........................5-4
California Proposition 65 Warning.....................5-5
California Perchlorate Materials Requirements.....5-5
Doing Your Own Service Work.........................5-6
Engine Fan Breakage.....................................5-6
Fuel................................................................5-7
Gasoline Octane............................................5-7
Gasoline Specifications....................................5-7
Additives.......................................................5-8
Diesel Engine Fuel.........................................5-9
What Fuel to Use...........................................5-9
Very Cold Weather Operation.........................5-12
Water in Fuel...............................................5-12
Running Out of Fuel.....................................5-17
Fuel Filter Replacement.................................5-18
Fuels in Foreign Countries.............................5-19
Filling the Tank............................................5-20
Filling a Portable Fuel Container.....................5-21
Checking Things Under the Hood....................5-22
Hood Latches...............................................5-22
Engine Oil (Caterpillar
®Diesel Engine).............5-23
Engine Oil (Gasoline Engine)..........................5-24
Engine Oil (DURAMAX
®Diesel Engine)............5-28Engine Oil (Isuzu Diesel Engine).....................5-32
Engine Oil Life System (Gasoline Engine)........5-36
Engine Oil Life System (DURAMAX
®/Isuzu
Diesel Engines).........................................5-37
Engine Oil Life System (Caterpillar
®Diesel
Engine)....................................................5-39
Engine Air Cleaner/Filter................................5-39
Automatic Transmission Fluid.........................5-43
Manual Transmission Fluid.............................5-43
Engine Coolant (Caterpillar
®Diesel Engines).....5-44
Engine Coolant (Gas and DURAMAX®/
Isuzu 7.8L L6 Engines)..............................5-44
Coolant Surge Tank Pressure Cap..................5-47
Engine Overheating.......................................5-48
Cooling System............................................5-50
Engine Fan Noise.........................................5-54
Power Steering Fluid.....................................5-54
Windshield Washer Fluid................................5-55
Brakes........................................................5-57
Battery........................................................5-66
Jump Starting...............................................5-67
Rear Axle.......................................................5-72
Rear Axle Shift Motor....................................5-73
Section 5 Service and Appearance Care
5-1