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The computer module is the heart
of the system
The computer is permanently pro-
grammed by factory engineers. The
program is a complex list of instructions
telling the computer how to control the
engine under various driving conditions.
To do its job, the computer needs to
know what is happening and then it
needs devices to control things.
Sensors give the computer
information
The computer can only work with
electrical signals. The job of the sensor
is to take something the computer needs
to know, such as engine temperature,
and convert it to an electrical signal
which the computer can understand. You
can think of sensors as “high tech”
senders - the devices found in older
vehicles for gauges and dashboard
message lights (oil pressure, fuel level,
etc). Signals running into the computer
are referred to as “inputs.”
Sensors monitor such things as:
• Engine temperature
• Intake manifold vacuum
• Throttle position
• RPM
• Incoming air (temperature, amount)
• Exhaust gas oxygen content
• EGR Valve flow
Most engine computer systems will use
the sensor types listed above. Additional
sensors may be used depending upon
the engine, vehicle type or other tasks the
computer must do. Note that information
from one sensor may be used by the
computer for many different tasks. For
example, engine temperature is
something the computer needs to know
when controlling fuel delivery, spark
timing, idle speed and emission systems.
The sensor information may be very
important for one engine control function,
but only used to “fine tune” a second one.
There are several types of sensors
•
Thermistor - This is a resistor whose
resistance changes with temperature.
It is used to measure temperatures of
coolant or incoming air. It has two
wires connected to it.
•
Potentiometer - This signals a
position, such as throttle position or
EGR valve position. It connects to
three wires: one for power, one for
ground and one to carry the position
signal back to the computer.
•
Switches - These are either ON
(voltage signal to the computer) or
OFF (no voltage signal to the
computer). Switches connect to two
wires and tell the computer simple
things, such as whether or not the air
conditioner is running.
•
Signal Generator - These create their
own signal to tell the computer of
some condition, such as exhaust gas
oxygen content, camshaft position, or
intake manifold vacuum. They may
have one, two or three wires con-
nected to them.
Actuators are energized by the
computer to control things
The computer can only send out
electrical signals (referred to as
“outputs”). Devices called actuators are
powered by the computer to control
things. Actuator types include:
•
Solenoids - These are used to control
a vacuum signal, bleed air, control fuel
flow, etc.
•
Relays - These switch high amperage
power devices on and off, such as
electric fuel pumps or electric
cooling fans.
•
Motors - Small
electric motors can be
used to control idle
speed.
OUTPUT
AC
TUA
TORS
SENSORS
INPUT
ECA
BRAINS OF THE
COMPUTER
Summary of Contents for Code Scanner CP9025
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