
The engine idle speed will return to normal once the
following conditions are met:
•Once engine coolant temperature reaches about
150°F (65°C).
•The intake temperature reaches a certain level.
The high idle speed will be temporarily interrupted and
the engine speed will return to normal if any of the
following conditions occur:
•The brake pedal is applied.
•The accelerator pedal is pressed.
•The automatic transmission is shifted out of
P (Park) or N (Neutral).
•The clutch pedal on the manual transmission is
pressed.
•Vehicle speed is detected.
Once these conditions no longer exist, the engine idle
speed will slowly increase to high idle after the
normal delay, if the conditions for engine coolant
temperature and air intake temperature are still met.
Engine Checks Before Operating
When you have started the engine, let it run for
20 to 30 seconds before you put a load on the engine.
But do not leave the vehicle while the engine is running.
Avoid unnecessary idling of diesel engine equipped
vehicles.
If the engine idles too long, the temperature of the
engine coolant will fall below the normal operating
range. Low engine operating temperature causes
several conditions which affect engine operation and
reduce engine life.
The engine should be permitted to go through a
warm-up period. Operate the vehicle at a minimum of
600 rpm during the warm-up period. During this
period and during operation, the following observations
should be made.
2-23

During this warm-up period, check the warning lights
and gages:
•If oil pressure does not begin to rise within
15 seconds of starting, stop the engine and find the
cause. SeeOil Pressure Gage on page 3-38for
more information.
•If the engine coolant temperature gage needle goes
into the hot area on the gage, stop the engine and
find the cause of the overheating. SeeEngine
Coolant Temperature Gage on page 3-34for more
information.
•If you have air brakes, the dual-needle air pressure
gage should read at least 115 psi (790 kPa) for both
service systems before you try to move the vehicle.
When air pressure is below 60 psi (420 kPa), the
LOW AIR light will come on and you will hear a
tone alarm. SeeBrake System Warning Light on
page 3-31for more information. If the pressure does
not build up or drops during warm-up, stop the
engine and find the cause before you try to move the
vehicle. Recommended air pressure before driving is
120 psi (830 kPa). SeeAir Pressure Gage on
page 3-47for more information.
•The charging system light should come on when the
ignition key is turned to ON/RUN or START and
should go out when the engine is running above idle.
If the light does not go out or comes back on during
normal engine operation, have the charging system
checked right away. (This light tells you if the
generator is not charging; it does not reflect the
condition of the battery.) SeeCharging System Light
on page 3-29for more information.
•The voltmeter charge indicator gage tells you the
condition of the battery’s charge. The gage should be
in the center area during engine operation. The red
area on the left indicates an undercharge condition;
the red area on the right indicates an overcharge.
If the gage is in either red area, have the battery and
charging system checked right away. SeeVoltmeter
Gage on page 3-30for more information.
Notice:Do not allow the engine to operate at low
idle for more than five minutes. This can cause low
engine operating temperatures which can affect
engine operation and reduce engine life. Engine idle
speed should be increased to 1200 rpm whenever
extended idle is required. Once started, the engine
should be placed under load to allow the engine
coolant temperature to reach 150°F (66°C) before
shutting off the engine.
2-24

Engine Coolant Heater
The engine coolant heater can provide easier starting
and better fuel economy during engine warm-up in cold
weather conditions at or below 0°F (−18°C). Vehicles
with an engine coolant heater should be plugged
in at least four hours before starting.
To Use the Engine Coolant Heater
1. Turn off the engine.
2. Find the plug-in outlet located under the driver door.
3. Plug it into a normal, grounded 110-volt AC
outlet.
{CAUTION:
Plugging the cord into an ungrounded outlet could
cause an electrical shock. Also, the wrong kind of
extension cord could overheat and cause a fire.
You could be seriously injured. Plug the cord into
a properly grounded three-prong 110-volt AC
outlet. If the cord will not reach, use a heavy-duty
three-prong extension cord rated for at least
15 amps.
4. Before starting the engine, be sure to unplug and
store the cord as it was before to keep it away
from moving engine parts, and prevent damage.
The length of time the heater should remain plugged in
depends on several factors. Ask a dealer/retailer in
the area where you will be parking the vehicle for the
best advice on this.
2-25

Diesel Engine Exhaust Brake
If the vehicle has a Isuzu 6H Diesel Engine, it may have
an exhaust brake, which is located in the exhaust
system.
If the vehicle has a 6.6L DURAMAX
®6600 or
Caterpillar®Diesel Engine, it may have an exhaust
brake, which is controlled through the turbocharger.
The exhaust brake for both engines operates the same.
The exhaust brake switch
is located in the instrument
panel switchbank.
Push the bottom of the switch to turn the exhaust brake
on. When you push the top of the switch, the exhaust
brake will turn off.
There is an indicator light on the instrument panel
similar to the symbol on the switch, that comes on when
the exhaust brake is active. SeeExhaust Brake
Indicator Light on page 3-41for more information.While using the exhaust brake, the proper gear range
selection is important. The exhaust brake is most
effective if the gear range selected is the lowest possible
range that does not allow the engine rpm to go more
than 200 rpm above rated (full load) rpm. If you have
a Caterpillar
®Diesel Engine, do not exceed 2900 rpm.
If you have an Isuzu 6H Diesel engine, do not
exceed 2550 rpm. If the vehicle has a DURAMAX
®
6600 Diesel Engine, do not exceed 3600 rpm.
If the vehicle has an Allison
®1000/2200/2300/2350/2500/
2550 series automatic transmission and this button is
pressed, the transmission downshifts to a factory default
setting of third gear. To change the default setting, or for
more information on factory default settings, contact your
dealer/retailer for assistance.
The accelerator and clutch pedals must be released in
order for the exhaust brake to engage. The exhaust
brake will automatically shut off when the antilock brake
system is active.
If the vehicle has a Caterpillar
®Diesel Engine or a
DURAMAX®6600 Diesel Engine, the exhaust brake will
become active in cruise control when you exceed the
set speed by 3 to 5 mph.
2-26

Automatic Transmission Operation
If the vehicle has an Allison®five-speed or six-speed
automatic transmission, you will also find an Allison®
Transmission Operator’s Manual in the vehicle which
goes into more detail. On the headliner, in front of and
above the driver, or in some other place near the driver,
you will see a label that describes important operating
facts about the automatic transmission in the vehicle.
Make sure you follow the instructions on this label.
Vehicles equipped with an Allison
®3000 Series
transmission come with a push button shift selector that
will display transmission information. Refer to the Allison
®
Transmissions Operator’s Manual for more information
on transmission diagnostics and shift selector operation.
Be sure to keep the parking brake set until you are
ready to shift into D (Drive). SeeParking Brake (With
Hydraulic Brakes) on page 2-38orParking Brake (With
Air Brakes) on page 2-41for parking brake procedure.
Press the brake pedal while shifting from N (Neutral) or
P (Park) to a drive gear.All vehicles with automatic transmission can be started
in P (Park), if equipped, or in N (Neutral). See the
Allison
®Transmission Operator’s Manual for additional
information.
{CAUTION:
It can be dangerous to get out of the vehicle
without the parking brake firmly set. The vehicle
can roll. If you have left the engine running, the
vehicle can move suddenly. You or others could
be injured. To be sure the vehicle will not move,
even when you are on fairly level ground, always
set the parking brake.
{CAUTION:
Shifting into a drive gear while the engine is
running at high speed is dangerous. Unless your
foot is firmly on the brake pedal, the vehicle could
move very rapidly. You could lose control and hit
people or objects. Do not shift into a drive gear
while the engine is running at high speed.
2-27

Overdrive Defeat
If your vehicle has this feature, you can select not to
shift up to fifth gear. This is useful when towing or under
a heavy load.
The overdrive defeat
switch is located in the
instrument panel to
the right of the steering
column.
Press the switch to limit the transmission to fourth gear.
This will allow for fewer downshifts while pulling a
trailer or under a heavy load. The indicator light in the
switch comes on whenever overdrive defeat is active.
If the vehicle is equipped with a push button shift
selector, refer to the Allison
®Transmission Operator’s
Manual for shift selector operating instructions.
Manual Transmission Operation
Using the Clutch
When you are starting to move the vehicle, it is
important to begin with the engine speed at idle. Then
start to engage the clutch and listen for an engine speed
drop of about 100 rpm. At this point, the clutch is
engaging, so you should increase the engine speed and
fully engage the clutch. It is important not to increase
the engine speed sooner or before the clutch begins its
engagement. If you do, you can cause damage to
the vehicle.
Double-Clutching
You must use the double-clutching method when you
shift an unsynchronized gear set. Disengage the clutch,
shift to N (Neutral) and engage the clutch. When
upshifting, slow the engine until the engine rpm and
road speed match. When downshifting, accelerate the
engine until the engine rpm and road speed match. Then
quickly disengage the clutch and move the shift lever
to the next gear position and engage the clutch.
2-28

Eaton®Fuller®Five and Six-Speed
Transmissions and TTC Spicer
Seven-Speed Transmissions
These transmissions have gears that automatically
synchronize when you shift up or down (except 1 (First)
gear on the five-speed and seven-speed transmission
which is unsynchronized). Choose the gear that will
maintain the road speed you want while keeping
the engine above two-thirds of the governed speed.
When the engine speed drops below two-thirds of the
governed speed, shift into the next lower gear before
your engine begins to lug. When you shift down, be sure
to double-clutch if required.
Eaton®Fuller®Nine and Ten-Speed
Non-Synchronized Manual
Transmissions
If the vehicle has one of these transmissions the engine
rpm and road speed must match when upshifting and
downshifting. The label above the windshield will tell you
the operating basics you need to know.
The following are driving tips.
•Always choose an initial starting gear suitable for
the load and terrain.
•Always use double-clutching procedures when
shifting.
•Never move the range shift lever to the LO speed
gear position after HI range preselection, or
anytime the transmission is in the HI range.
•Never move the range knob or lever with the shift
lever in N (Neutral) while the vehicle is moving.
•Never make a range shift while moving in
R (Reverse).
Clutch Brake (Vehicles with
Non-Synchronized Transmission)
A clutch brake is used to stop transmission input shaft
rotation so that 1 (First) or R (Reverse) gear selection
can be initiated when the vehicle is at a standstill
and the engine is idling.
Press the clutch pedal all the way down to the floorboard
to apply the clutch brake.
When using the clutch brake, disengage the clutch pedal
and shift the transmission into either the initial starting
gear or R (Reverse). If the tooth-butting occurs between
the clutching teeth, re-engage the clutch while applying
light pressure to the shift lever. This will provide for a
smooth shift into either 1 (First) or R (Reverse) gear.
Notice:Using the clutch brake for shifting into any
gear other than 1 (First) or R (Reverse) may cause
premature wear of the clutch brake and make gear
shift effort more difficult. Do not use the clutch brake
for shifting after engaging 1 (First) or R (Reverse).
2-29

Power Take-Off (PTO)
The vehicle may have
power take-off (PTO). The
PTO switch is located
on the instrument panel.
An indicator in the switch comes on to show PTO is
active. SeeHigh Idle System on page 2-20for
more information.
A PTO is a gearbox or mechanical device used to
transmit mechanical power from the powertrain, through
gears or a transmission, to another mechanical or
hydraulic device. Before using a PTO, refer to the
manufacturer’s or installer’s instructions.
Four-Wheel Drive
If the vehicle has four-wheel drive, you can send the
engine’s driving power to all four wheels for extra
traction. To get the most satisfaction out of four-wheel
drive, you must be familiar with its operation. Read
the part that follows before using four-wheel drive. You
should use two-wheel drive high for most normal
driving conditions.
Notice:Driving on clean, dry pavement in
four-wheel drive for an extended period of time can
cause premature wear on the vehicle’s powertrain.
Do not drive on clean, dry pavement in Four-Wheel
Drive for extended periods of time.
2-30