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Pull off the road and shut off the engine. Do
not start it until the reason for the problem is
known, and the problem is fixed. If the engine
shuts down when you are still in traffic, you can
restart the engine and get another 25 to
30 seconds of operation. Do this only if you have
to, since there is a problem that can harm the
engine if it is not fixed. Engine automatic
shutdown, for gasoline engines, requires activation
by your dealer.
Notice:If you try to operate the vehicle after
the engine automatically shuts down, you
may damage the vehicle. Have your vehicle
repaired as soon as possible.Ambulance, Fire, and Rescue Packages
Your check gages warning light will come on if
the system senses high engine temperature or low
engine oil pressure. If high engine temperature
or low engine oil pressure is detected, you will also
hear a tone alarm at two beats per second. The
alarm and the light will remain on until the
condition is fixed. If the engine temperature or oil
pressure condition worsens, the tone alarm
will go to five beats per second.
If the system senses low engine coolant, the
five beat per second alarm and the low coolant
warning light will come on.
The engine will not shutdown, but you should
have the vehicle checked as soon as you can.
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Page 106 of 430

High Idle System
High Idle System with Switch
If your vehicle has this
feature, the manual high
idle switch is located
in the instrument panel
switchbank.
This system can be used to increase your engine
idle speed whenever the following conditions
are met:
•The brake pedal is not pressed.
•The vehicle speed is below about 5 mph
(8 km/h) for vehicles with diesel engines. The
vehicle must not be moving and the
accelerator must not be pressed for vehicles
with gasoline engines.
•If the vehicle has manual transmission the
clutch pedal is not pressed or, if the vehicle
has the automatic transmission it is in
NEUTRAL (N) or PARK (P).
The manual high idle feature is activated by
pressing the switch on the instrument panel. When
the switch is pressed again, or any of the
previous conditions are not met, manual high idle
will be deactivated.
The manual high idle has been preset at the
factory. Your dealer may change the setting to fit
your needs.
For vehicles with Caterpillar
®diesel engines, the
high idle switch can be used to set any desired
high idle speed.
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To set a new temporary engine idle speed do the
following:
1. Make sure all of the previously described
conditions are met.
2. Press the accelerator pedal to the desired
engine speed.
3. Momentarily press the manual high idle
switch.
The temporary high idle speed will be set. This
new high idle rpm level will be remembered by the
system until either the ignition is turned to OFF
or a new high idle speed is set.
Automatic High Idle System
The automatic high idle feature will engage
whenever you start your vehicle and the engine is
below the preset operating temperature. This
will help decrease engine warm-up time.On vehicles that have the Caterpillar
®diesel
engine you may have an exhaust restrictor that
will operate in High Idle mode. The exhaust brake
switch must be on for this feature to operate.
SeeDiesel Engine Exhaust Brake on page 112for
more information.
Idle speed will then return to normal under any of
the following conditions:
•The engine reaches the preset operating
temperature or has been operating for at least
10 minutes.
•The brake pedal is pressed.
•The manual transmission clutch pedal is
pressed or, if the vehicle has automatic
transmission, it is shifted from NEUTRAL (N)
or PARK (P).
•The vehicle speed exceeds about 5 mph
(8 km/h).
•The throttle is pressed.
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Page 108 of 430

Exhaust Restrictor
(Engine Warm-Up)
Exhaust Restrictor
If your vehicle has a Isuzu 6H or Caterpillar®
Diesel Engine, it may have a feature called
an Exhaust Restrictor (NPE), which uses an air
actuated valve in the exhaust system to restrict
exhaust gas flow which enhances the engine and
heater warm-up.
Automatic Quick Warm-Up
If your vehicle has a DURAMAX®6600 engine, it
has a feature called an Automatic Quick
Warm-Up, which uses the turbocharger to restrict
the exhaust gas flow which enhances the
engine and heater warm-up.
In both systems, exhaust restrictor or automatic
quick warm-up, the cold temperature high
idle feature elevates the engines idle speed, up to
1500 rpm, and restricts the exhaust gas flow,
when outside temperatures are below 32°F (0°C),
and the engine coolant temperature is below
certain levels. This feature enhances heater
performance by raising the engine coolant
temperature faster.For all engines this feature is already turned on.
The automatic quick warm-up on the DURAMAX
®
engine can be turned off and on by doing the
following procedure:
1. Turn the ignition to RUN, with the vehicle off.
2. Press the accelerator pedal to the floor
and hold it while quickly pressing and
fully releasing the brake pedal three times in
less than eight seconds.
3. Release the accelerator pedal and start the
engine. The green exhaust brake/restrictor
light below the radio controls will be lit
for 10 seconds.
If this feature is turned off, by doing the
procedure described previously, and then the
engine is started, the exhaust brake/restrictor
light will flash for 10 seconds and then it
will turn off.
When the engine is started, it will slowly increase to
the high idle speed after a delay of a few seconds;
up to about two minutes. For this method to work
properly there must be no throttle or brake pedal
faults, and the throttle pedal must not fall below
75 percent of wide open throttle while pressing the
brake pedal.
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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
PARK (P) or NEUTRAL (N).
•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 your 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.
During this warm-up period, check your 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 175for more information.
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•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 173for 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 169for 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 183for
more information.
•The charging system light should come on
when the ignition key is turned to 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 thegenerator is not charging; it does not reflect
the condition of the battery.) SeeCharging
System Light on page 167for more
information.
•The voltmeter charge indicator gage tells you
the condition of your 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 168
for more information.
Notice:Do not allow the engine to operate at
low idle for more than ve 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.
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Engine Coolant Heater
Your vehicle may be equipped with this feature.
In very cold weather, 0°F (–18°C) or colder,
the engine coolant heater can help. You will get
easier starting and better fuel economy during
engine warm-up. Usually, the coolant heater
should be plugged in a minimum of four hours
prior to starting your vehicle. At temperatures
above 32°F (0°C), use of the coolant heater is
not required.
To Use the Engine Coolant Heater
1. Turn off the engine.
2. Find the plug-in outlet located under the
driver’s 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 re. 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. If you do
not, it could be damaged.
How long should you keep the coolant heater
plugged in? The answer depends on the outside
temperature, the kind of oil you have, and some
other things. Instead of trying to list everything here,
we ask that you contact your dealer in the area
where you will be parking your vehicle. The dealer
can give you the best advice for that particular area.
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Page 112 of 430

Diesel Engine Exhaust Brake
If your vehicle has a Isuzu 6H or Caterpillar®
Diesel Engine, it may have an exhaust brake,
which is located in the exhaust system.
If your vehicle has a 6.6L DURAMAX
®6600
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 will come
on when the exhaust brake is active. SeeExhaust
Brake Indicator Light on page 178for more
information.When using the exhaust brake, the proper gear
range selection is important. The exhaust brake will
be 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 a
Isuzu 6H Diesel engine, do not exceed 2550 rpm.
If you have a DURAMAX
®6600 Diesel Engine, do
not exceed 3600 rpm.
If your vehicle has an Allison
®
1000/2200/2300/2500 series automatic
transmission and press this button, the
transmission will downshift to a factory default
setting of third gear. To change the default setting,
or for more information on factory default
settings, contact your dealer 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 anti-lock brake system is active.
If your 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.
112