Actron Ford Code Scanner CP9015 - Manual (Page 52)

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(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 connected to
them.
The computer controls things
with Actuators
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 motors are often used
to control idle speed.
Other output signals
Not all of the computer outgoing signals
go to actuators. Sometimes information is
sent to electronic modules, such as
ignition or trip computer.
How the computer controls
Fuel Delivery
Operation and emission performance
depend upon precise fuel control. Early
computer controlled vehicles used
electronically adjustable carburetors, but
fuel injectors were soon introduced.
The job of the computer is to provide the
optimum mixture of air and fuel (air/fuel
ratio) to the engine for best performance
under all operating conditions.
The computer needs to know:
• ...what the engine operating condition
OUTPUT
AC
TUA
TORS
SENSORS
INPUT
ECA
BRAINS OF THE
COMPUTER