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 2-27for 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.
Exhaust Restrictor
(Engine Warm-Up)
Exhaust Restrictor
If your vehicle has a DURAMAX®7800 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 with 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.
2-22
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.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.
2-23
Diesel Engine Exhaust Brake
If your vehicle has a DURAMAX®7800 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 3-41for 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®7800 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.
2-27
Two-Speed Rear Axle Electric Shift
Control
If your vehicle has this feature, you will find a label on
the headliner above the windshield or in another
place near the driver that shows how to use it. Be sure
to follow the directions carefully.
Use the following directions based on the type of shift
control the vehicle has.
The rear axle shift control
switch for a manual
transmission is located on
the shift lever.
When the switch is down, the rear axle is in the high
range. When the switch is up the rear axle is in
low range. Push or pull the switch to change the range.The two-speed axle should be in the up position or low
range when you park the vehicle. You will need to
engage the transmission and move the vehicle a little to
assure the axle is in the low range. Then apply the
parking brake, shift into NEUTRAL and shut off
the engine.
Also, always start the vehicle in motion with the
two-speed axle in the low range.
To shift up from low to high, do the following:
1. Move the switch down for the high range.
2. Disengage the clutch.
3. After a brief pause, engage the clutch and then
press down on the accelerator pedal until the
axle engages.
To shift down from high to low, do the following:
1. Release the accelerator and pull the switch upward
for low range.
2. Press the accelerator pedal slowly until the axle
engages.
2-28
Air Shift Control
(Automatic Transmission)
The rear axle shift control
switch for an automatic
transmission is located in
the instrument panel
switchbank.
To use the rear axle shift control, press the bottom of
the switch to get to the high range. The switch indicator
light will come on when the vehicle is in the high
range. Press the top of the switch to return to the low
range.
The two-speed axle should be in low range when
you park the vehicle. You will need to engage the
transmission and move the vehicle a little to assure the
axle is in range. Then shift into PARK (P), apply the
parking brake, and shut off the engine.To shift up from low to high range while driving, press
the bottom of the rear axle shift control switch as you are
releasing the accelerator pedal. After the shift has
occurred, apply the accelerator as desired.
To shift from high to low range while driving, press the
top of the rear axle shift control switch as you release
the accelerator pedal. Press the accelerator pedal slowly
until the down shift has occurred, then apply the
accelerator as desired.
For better performance during off-road or under a heavy
load, shift the axle into low range and then operate
the transmission normally.
For better performance on the highway, shift the axle to
high range and operate the transmission normally.
2-29
Automatic Transmission Operation
We build vehicles with Allison®five and six-speed
automatic transmissions. This part of the manual covers
the basics of these. With these transmissions, you
will find another Allison
®manual in your vehicle that
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
your vehicle. Make sure you follow the instructions on
this label.
Be sure to keep your parking brake set until you are
ready to shift into DRIVE (D), and press the brake pedal
while shifting from NEUTRAL (N) or PARK (P) to a
drive gear.
All vehicles equipped with automatic transmissions can
be started in PARK (P), if equipped, or in NEUTRAL (N).
See the Allison
®Transmission Operator’s Manual in
your vehicle for more information about this.
{CAUTION:
It can be dangerous to get out of your vehicle
without the parking brake rmly set. Your
vehicle can roll. If you have left the engine
running, the vehicle can move suddenly. You
or others could be injured. To be sure your
vehicle will not move, even when you are on
fairly level ground, always set the parking
brake.
{CAUTION:
Shifting into a drive gear while your engine is
running at high speed is dangerous. Unless
your foot is rmly on the brake pedal, your
vehicle could move very rapidly. You could
lose control and hit people or objects. Do not
shift into a drive gear while your engine is
running at high speed.
2-30
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 will come on whenever overdrive defeat is active.
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
your vehicle.
Double-Clutching
You must use the double-clutching method when you
shift an unsynchronized gear set. Disengage the clutch,
shift to 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.
2-31
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
FIRST (1) 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.
ZF Six-Speed Transmission
Here is how to operate your transmission.
This six-speed pattern is
unique to GM manual
transmissions.
The transmission always repositions the shift lever to
NEUTRAL, which is located between FOURTH (4)
and FIFTH (5) gear.
To prevent unintentional gear selections, additional force
is required to move the shift lever into REVERSE (R) or
FIRST (1). Use FIRST (1) when trailer towing, driving
with a heavier payload or launching on a grade.
Otherwise, start in SECOND (2) gear. Only shift into
FIRST (1) when the vehicle has stopped moving.
During the first 500 miles (805 km) of vehicle use, start
the vehicle moving in FIRST (1) gear. This allows
the clutch components to wear-in properly.
2-32