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Computerized vehicle control systems are made up of three basic component
groups. These groups are:
1. Sensors:
they are input devices that supply information about engine
operating conditions and the surrounding environment to the vehicle
computer.
2. Engine Control Module:
a vehicle computer that processes the information
supplied by the sensors, then sends an electronic command to the appropriate
components actuators.
3. Actuators:
these are output devices that may be electrical, mechanical or
vacuum components controlled by the vehicle computer.
Typical Sensors
Typical Actuators
Basic Diagnostics for the computer
Controlled Engine
There are two important steps that must always be followed when diagnosing
and repairing vehicles with computer controls.
·
Do basic engine diagnostics first .Many problems can be traced to lack of
routine maintenance on components such as plug wires, filters and spark plugs .
Also check for vacuum leaks on any vehicle, new or old, A completes engine
diagnosis should precede any electrical system diagnostics.
·
Follow the published diagnostic Charts Exactly through every step to mark a
repair on computer component.
Self-Diagnostic Computer Systems
One of the functions of the vehicle computer is to record fault codes produced
when a sensor or actuator fails. These failures are usually displayed as a
“Current Code” or as an “Intermittent Failures”. Be aware, however, that some
vehicle manufacturers use different terminology and older vehicles do not have
all of ground of codes described.
Current Codes
are faults that are active.
·
Hard Failure
causes the dash
“check engine” light to remain ON.
·
Intermittent Failure causes the dash
“check engine” light to flicker and then go
OFF after a short period of time. Generally the trouble code stays in the
computer memory.
History Codes
are stored codes for faults that have occurred in the past.
Failure Codes
When a failure is detected be the computer, it stores the information in the form
of
“Fault Codes” (also known as Trouble Codes or Service Codes). These Fault
Codes are usually a two or three digit number that identifies the electrical circuit
effected. Once these codes have been read the vehicle repair can be stares.
Be sure to closely follow the vehicle service manual diagnostic procedures,
repairs and specifications.
Component Testing
Component testing with a meter generally requires detailed schematics and
specifications that are provided by the manufacture. The following section
provides general information for the main groups of sensors (input) devices and
actuators (output) devices.
The primary input devices (sensors) are:
·
Temperature sensors
·
2-wire devices
·
3-wire devices
·
Oxygen sensor
·
pressure sensors
Primary output devices (actuators) are a form of an electromagnet that is either
ON or OFF. The ON/OFF signal, in general , will be in one of three
configurations:
·
ON of OFF only (switch)
·
Pulse width in a specified length of time (fuel injector)
Coolant
Sensor
Vacuum
Sensor
Throttle
Position
Sensor
RPM
Barometric
Sensor
Oxygen
Sensor
Eleatro
Mechonic
al
carburelor
Fuel
injoctio
n
Ignltion
Spark
advance
Exhaust Gas
Recirculeting
Valva
Air
Pump
Canister
Purge
Torque
Converter
clutch
Vehicle
Computer
