Allison Transmission Electronic Controls; Transmission Retarder; Engine Brake - PREVOST X3-45 VIP 2015 Owner's Manual

5-22 Other Features
ALLISON TRANSMISSION
ELECTRONIC CONTROLS
The Allison Transmission electronic controls
have four major elements:
Control Module (TCM), the Throttle Position
Sensor (TPS), speed
transmission shift selector control pad. Refer to
"Controls & Instruments"
components work together to electronically
control the functions of the transmission. The
throttle sensor, speed sensors and shift selector
transmit information to the TCM. The TCM
processes this information and then sends
signals to actuate specific solenoids located on
the control valve body in the transmission. The
action of the solenoids affects hydraulic circuits,
which in turn control the upshifts, downshifts,
and lock-up functions. In addition to controlling
the operation of
transmission electronic controls monitor the
system for abnormal conditions.
When one of these conditions is detected, the
Allison electronic control system is programmed
to automatically respond in a manner which is
safe for the driver, the vehicle and the
transmission. The Allison electronic control
system turns ON the CHECK TRANS light on
the dashboard, which serves as a fault indicator.
To enhance troubleshooting and to allow
interrogation of the TCM for valuable service
information, the shift selector display on the
transmission control
diagnostic tool can be used. For information
about reading and interpreting diagnostic codes,
refer to Appendix C, "Allison Transmission
Diagnostic Troubleshooting Codes (DTC)".

TRANSMISSION RETARDER

The transmission retarder is an optional device
that helps to reduce the speed of a vehicle. It
improves vehicle control, increases driving
safety and permits more economical operation.
The retarder provides slowing power when it is
most needed, such as
mountain roads, in stop-and-go traffic and on
crowded freeways.
The transmission retarder is a vehicle-slowing
device, not a vehicle-stopping device. It is not a
substitute for the service braking system. The
service brake must be used to bring the vehicle
to a complete stop.
The retarder is provided with control buttons on
the steering wheel and a lever on the steering
column (refer to "
CONTROLS AND INSTRUMENTS
chapter).
The Transmission
sensors and
chapter. These
the transmission,
pad or an optional
when descending
NOTE
Extended use will raise the temperature of the
transmission oil.
The retarder helps to reduce speed on grades
without using the vehicle's conventional service
the
braking system. A retarder greatly increases the
service life of brake pads and discs, resulting in
reduced brake maintenance costs.
NOTE
The stoplights automatically illuminate when
the vehicle is slowing down due to the
application of the transmission retarder.
NOTE
For vehicles equipped with the Antilock
Braking System (ABS), as the wheels start to
lock-up on slippery roads, the output retarder
the
automatically deactivates until the wheels roll
freely.

ENGINE BRAKE

WARNING
A vehicle speed retarding device (such as
engine brake) is not intended to replace the
service brake systems on your vehicle nor
intended to bring your vehicle to a stop. A
vehicle speed
intended to reduce the speed of your vehicle
under certain conditions.
Several types of engine brake can be installed
or are standard on certain engines. All are
used to reduce wear on the vehicle brake
linings.
WARNING
When descending significant grades, use the
service brake as little as possible. If the
engine does not slow the vehicle to a safe
speed, apply service brake and shift to a lower
range. Let the engine (and engine brake) slow
the vehicle. Keep brakes cool and ready for
emergency stopping.
"
retarding device is only