DIAGNOSTIC MANUAL
Ohm (Ω)
The unit of electrical resistance. One ohm is the value of resistance through which a potential of one volt will
maintain a current of one ampere. (SAE J1213 NOV82)
Oxides of Nitrogen (NOx)
Nitrogen oxides formed by a reaction between nitrogen and oxygen at high temperatures.
Oxygen Sensor (O
2
S)
A sensor that monitors oxygen levels in the exhaust.
Particulate matter
Particulate matter includes mostly burned particles of fuel and engine oil.
Piezometer
An instrument for measuring fluid pressure.
Power
Power is a measure of the rate at which work (force x distance) is done during a specific time. Compare
with Torque.
Power TakeOff (PTO)
Accessory output, usually from the transmission, used to power a hydraulic pump for a special auxiliary
feature (garbage packing, lift equipment, etc).
Pulse Width Modulation (PWM)
Succession of digital electrical pulses, rather than an analog signal. Efficient method of providing power
between fully on and fully off.
Random Access Memory
(RAM)
Computer memory that stores information. Information can be written to and read from RAM. Input
information (current engine speed or temperature) can be stored in RAM to be compared to values stored in
Read Only Memory (ROM). All memory in RAM is lost when the ignition switch is turned off.
Rated gross horsepower
Engine gross horsepower at rated speed as declared by the manufacturer. (SAE J1995 JUN90)
Rated horsepower
Maximum brake horsepower output of an engine as certified by the engine manufacturer. The power of
an engine when configured as a basic engine. (SAE J1995 JUN90)
Rated net horsepower
Engine net horsepower at rated speed as declared by the manufacturer. (SAE J1349 JUN90)
Rated speed
The speed, as determined by the manufacturer, at which the engine is rated. (SAE J1995 JUN90)
Rated torque
Maximum torque produced by an engine as certified by the manufacturer.
Reference voltage (V
REF
)
A 5 volt reference supplied by the ECM to operate the engine sensors.
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