85
Mode
A type of operating condition,
such as “idle mode” or “cruise
mode.”
M/T
Manual Transmission or Manual
Transaxle.
Neutral switch
This switch is mounted on the
Manual transmission/Transaxle.
It signals the ECU when the
gearshift lever is in the Neutral
position.
O
2
Oxygen. See Oxygen sensor.
Open (circuit)
A break in the continuity of a
circuit such that no electrical
current can flow.
Open Loop (O/L)
This is when a control system
performs an action (expecting a
certain result), but has no way
of verifying if the desired results
were achieved. Example: The
ECU pulses a fuel injector
expecting a certain amount of
fuel to be delivered. (The ECU
assumes everything in the fuel
system is operating as
expected.) In open loop
operation, the ECU has no way
of checking the actual amount
of fuel delivered. Thus, a faulty
injector or incorrect fuel
pressure can change the
amount of fuel delivered and the
ECU would not know it.
Outputs
Electrical signals sent from the
ECU. These signals may
activate relays or other
actuators for control purposes
around the vehicle. The signals
can also send information from
the ECU to other electronic
modules, such as ignition or trip
computer.
Oxygen Sensor (O
2
Sensor)
The Oxygen (O
2
) sensor
measures the amount of oxygen
in the exhaust gas and signals
the ECU. The ECU uses this
information to maintain the
correct Air/Fuel ratio.
PA Sensor
(Pressure - Atmosphere.) See
Atmospheric Pressure Sensor.
Park Switch
Informs the ECU when the
gearshift lever is in the Park
position.
PCV
See Positive Crankcase
Ventilation.
PFI
See Port Fuel Injection.
PGM-FI
See Programmed Fuel Injection.
Port Fuel Injection
(PFI)
A fuel injection system using
one injector per cylinder. These
injectors are mounted in the
intake manifold and usually fired
in groups.
Positive
Crankcase
Ventilation (PCV)
The PCV valve allows blow-by
gases from the engine’s
crankcase to be drawn into the
intake manifold and into the air
cleaner to be burned in
combustion.
Power Transistor
A heavy duty transistor usually
used as an electronic switch to
control loads such as the
ignition coil.
Power Transistor
Relay
Supplies power to ignition
coil(s).
Pressure
Regulator Valve
(PRV)
Maintains proper fuel pressure
in the fuel rail for the fuel
injectors.
Programmed Fuel
Injection (PGM-FI)
A Fuel Injection system in which
a control unit identified as an
ECU, (or similar name), adjusts
the amount of fuel injected into
the cylinder or throttle body
based upon information from
various sensors.
PRV
See Pressure Regulator Valve.
Pulse Generator
See TDC/CRANK/CYL.
Relay
A mechanical device for
switching high current circuits
on and off. It is electronically
controlled by a low current
circuit. Relays allows a low
power ECU signal to control a
high power device such as an
electric cooling fan.
Resistor
An electronic device that limits
electrical current flow.
ROM
Read-Only Memory. This is
inside the ECU. The ROM
contains permanent
programming information the
ECU needs to operate a
specific vehicle model. Included
are vehicle weight, engine and
transmission type, axle ratio
and other specifics.
Safety Relay
Supplies power to the fuel
pump relay and protects some
electronic components from
being damaged by reverse
battery polarity.
Sensor
Device which give the ECU
information. The ECU can only
work with electrical signals. The
job of the sensor is to take
something the ECU needs to
know, such as engine
temperature, and convert it to
an electrical signal which the
ECU can understand. The ECU
uses sensors to measure such
things as throttle position,
coolant temperature, engine
speed, incoming air, etc.
SFI
See Sequential Fuel Injection.
Sequential Fuel
Injection (SFI)
Also referred to as Sequential
Electronic Fuel Injection. A fuel
injection system using one
injector for each cylinder. The
Summary of Contents for Code Scanner CP9025
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