•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. If the pressure doesn’t
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 actually
driving away is 120 psi (830 kPa).
•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 doesn’t 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 doesn’t
reflect the condition of the battery.)
•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.Notice:For diesel engines, don’t 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.
Engine Coolant Heater
If your vehicle has this
feature, the plug-in
receptacle is located under
the driver’s door.
In very cold weather, 0°F (−18°C) or colder, the engine
coolant heater can help. You’ll get easier starting
and better fuel economy during engine warm-up.
2-23
Diesel Engine Exhaust Brake
The exhaust brake is available on vehicles equipped
with a diesel engine. It is located in the exhaust system.
The exhaust brake is used to help slow the vehicle
and may assist the vehicle’s foundation brakes. The use
of the exhaust brake will assist the braking of the
vehicle and prolong the life of the foundation brake
lining material.
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 3-40for 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 DURAMAX™ (LG4) diesel
engine, do not exceed 2400 rpm. If you have a
DURAMAX™ (LB7) diesel engine, do not exceed
3600 rpm.
If you have an automatic transmission and press this
button, the transmission will downshift to a factory
default setting of fourth 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 not function when the cruise control feature is
active, and will automatically shut off when the
anti-lock brake system is active.
2-25
Parking
{CAUTION:
If you don’t park your vehicle properly, it can
roll. If you’ve left the engine running, it can
move very quickly. You or others could be
injured. To be sure your vehicle won’t move,
even when you’re on level ground, follow the
steps below.
Two-Speed Rear Axle
1. With the engine running, shift the two-speed rear
axle into low. To be sure it’s in low, you’ll need to
move the vehicle in gear just a little.
2. Hold the regular brake pedal down with your
right foot.
3. Apply the parking brake.
4. Shift the transmission to NEUTRAL or PARK (P).
Hydraulic Brakes
If your vehicle has hydraulic brakes, it has either a
parking brake foot pedal or hand lever. If you have the
parking brake foot pedal, it is located below the
instrument panel to the left of the steering column.
If you have the parking brake hand lever, it is located to
the right of the driver, on the floor.
To set the foot pedal parking brake, hold the regular
brake pedal down with your right foot. Push down
the parking brake pedal with your left foot.Parking Brake Hand Lever
2-33
Air Brake
{CAUTION:
When the yellow SYSTEM PARK and the red
TRAILER AIR SUPPLY knobs are both pushed
in, your rig will be free to move. It could strike
someone or something. When both of these
knobs are pushed in, hold the regular brake
pedal down to keep your rig from moving.
If your vehicle has air
brakes, you will have this
parking brake. It is
located above the radio in
the instrument panel.
Pulling it out applies the parking brake. The park brake
light will come on when the air parking brake is
applied.Vehicles built for use as tractors or towing vehicles have
two air brake controls. They look like this:
To charge a trailer’s air brake system do the following:
1. Move your tractor into the proper position.
2. Apply the parking brake by pulling the yellow
parking brake knob out.
3. Hook up the trailer air system properly.
4. Get into the tractor.
5. Push and hold down the regular brake pedal.
6. Push in both the yellow parking brake and the red
trailer air supply knobs. This will charge your
trailer’s air system.
2-35
After a few minutes, the trailer system should be fully
charged. When it is, the air pressure gage will show
about 125 to 135 psi (862 to 931 kPa).
For driving with a trailer, the yellow and red (if equipped)
knobs must be pushed in. It’s the same when you’re
not pulling a trailer except that the red trailer air supply
knob must be pulled out.
{CAUTION:
If you apply any one of the air brake parking
controls while the vehicle is moving, your rig
will stop suddenly. If you are not ready for
this, you or others could be injured. Don’t
apply any one of these controls while you’re
driving, unless you have to make an
emergency stop.
If the air pressure drops below 60 to 70 psi
(413 to 482 kPa), the primary brake light and warning
buzzer will come on. If the air pressure drops to
35 to 45 psi (241 to 310 kPa), the red trailer air supply
knob will automatically pop out and apply the spring
brakes on the trailer.If the air pressure drops to 35 to 45 psi (241 to 310 kPa),
the yellow park brake knob will automatically pop out
and apply the spring brakes on the truck or tractor.
If you ever have a complete loss of air so that your air
brakes automatically apply, there is a way that the
tow operator can release the parking brakes to tow the
vehicle. SeeTowing Your Vehicle on page 4-31.
{CAUTION:
If your vehicle is left in gear, the engine can
start if the vehicle starts to roll. This can easily
happen if you have the diesel engine. Shift the
transmission into NEUTRAL (N) before you
leave the vehicle.
2-36
Your hazard warning
flashers button is located
on top of the steering
column.
Your hazard warning flashers work no matter what
position your key is in, and even if the key isn’t in.
Press the button to make the front and rear turn signal
lamps flash on and off. Press the button again to
turn the flashers off.
When the hazard warning flashers are on, your turn
signals won’t work. The hazard warning flashers will not
flash if the brakes are applied.Other Warning Devices
If you carry reflective triangles, you can set one up at
the side of the road behind your vehicle in the
recommended manner per Federal Motor Carrier Safety
Regulation (FMCSR) Section 392.22, to warn others.
Horn
Sound the horn by pushing the center of the steering
wheel. If you have the optional air horn, it is controlled
by a cord that you’ll find up above and to the left of
the driver. The harder you pull on the cord, the louder
the air horn will sound. The air horn works only after
your air brake system pressure gets up to about
115 psi (790 kPa). The air horn will work properly
unless the the air brake system pressure drops below
60 psi (415 kPa).
3-6
Cruise Control
If your vehicle has this
feature, it is located at the
end of the multifunction
lever.
T(Set):Pressing in this button at the end of the
lever sets the cruise control speed.
9(Off):Moving the switch to this position turns off
the cruise control.
R(On):Moving the switch to this position turns on the
cruise control.
S(Resume/Accelerate):Moving the switch to this
position turns on resume/accelerate.With cruise control, you can maintain a speed of about
30 mph (48 km/h) or more without keeping your foot
on the accelerator. Cruise control does not work
at speeds below about 30 mph (48 km/h).
If you have an automatic transmission and you apply
your brakes, the cruise control will shut off.
If you have a manual transmission and you apply your
brakes or push the clutch pedal, the cruise control
will shut off.
{CAUTION:
Cruise control can be dangerous where you
can not drive safely at a steady speed. So, do
not use your cruise control on winding roads
or in heavy traffic.
Cruise control can be dangerous on slippery
roads. On such roads, fast changes in tire
traction can cause needless wheel spinning,
and you could lose control. Do not use cruise
control on slippery roads.
3-10
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 a GM dealer for service. If you
cannot drive to a dealer immediately, have the
vehicle towed.
Range Inhibit Warning Indicator
If your vehicle has an Allison
1000/2000/2200/2400 series automatic transmission, a
lighted bar under the current gear selected will flash.
If your vehicle has an Allison MD 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.
3-31