Illustration 4 Example Of Pulse Width Modulation

TM 9-2320-312-24-2

Systems Operation Section

Original Equipment Manufacturer (OEM) An OEM

is the manufacturer of a vehicle that utilizes a

Caterpillar engine.

Parameter A parameter is a programmable value

which affects the characteristics or the behavior of

the engine and/or vehicle.

Parameter Identifier (PID) A PID is a numerical

code that contains two digits or three digits. A

numerical code is assigned to each component.

The numerical code identifies data via the data link

to the ECM.

Password A password is a group of numeric

g00284479

Illustration 4

characters or alphanumeric characters. A password

is designed to restrict the changing of information

Example Of Pulse Width Modulation

in the ECM. The electrical engine systems require

Rated Fuel Position ("Rated Fuel Pos" on ECAP)

correct customer passwords in order to change

The rated fuel position indicates the maximum

customer specified parameters. The electrical

allowable fuel position (longest injection pulse). The

engine systems require correct factory passwords

rated fuel position will produce rated power for this

in order to clear certain logged events. Factory

engine configuration.

passwords are also required in order to change

certain engine specifications.

Reference Voltage The reference voltage is a

regulated voltage that is used by the sensor in order

Personality Module The personality module is

to generate a signal voltage.

the module in the ECM which contains all the

instructions (software) for the ECM and performance

Sensor A sensor is used to detect a change in

maps for a specific horsepower family. Updates and

the pressure, in the temperature, or in mechanical

rerates are accomplished by electronically flashing

movement. When any of these changes are

in new data. The updates and rerates are flashed in

detected, a sensor converts the change into an

using an electronic service tool.

electrical signal.

Power Take-Off (PTO) The PTO is operated with

Service Program Module (SPM) The SPM is a

the cruise control switches or dedicated PTO inputs.

software program on a computer chip that was

This mode of operation permits setting constant

programmed at the factory. The computer chip

engine rpm when the vehicle is not moving or when

is designed to adapt an ECAP for a particular

the vehicle is moving at slow speeds.

application.

Progressive Shifting Progressive shifting is

Short Circuit A short circuit is an electrical circuit

upshifting through the lower gears quickly. Shifts

that is mistakenly connected to an undesirable

are made above peak torque but below rated rpm.

point. For example, an electrical contact is made

Needlessly operating the engine in the higher rpm

with the frame whenever an exposed wire rubs

ranges before shifting to the next gear wastes fuel.

against a vehicle's frame.

Also, this mode of operation fails to take advantage

of the torque rise of the engine.

Signal A signal is a voltage or a wave that is

used to transmit information that is typically from a

Pulse Width Modulation (PWM) A PWM is a digital

sensor to the ECM.

type of electronic signal that corresponds to a

measured variable. The length of the pulse (signal)

Speed Burp A speed burp is a sudden brief

is controlled by the measured variable. The variable

change in engine rpm.

is quantified by a certain ratio. This ratio is the

percent of "on-time" that is divided by the percent

The speed-timing sensor is

Speed-timing Sensor

of "off-time". A PWM signal is generated by the

a sensor that provides

a Pulse Width Modulated

Throttle Position Sensor.

signal to the ECM. The

ECM interprets this signal as

the crankshaft position

and the engine speed.

Subsystem A subsystem is a part of the engine

system that relates to a particular function.