User's Manual

LAUNCH X-431Tool User’s Manual
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About ECU
In the last two decades, we have seen more
and more extensive application of IT and
electronic technologies in modern vehicles.
Many vehicle control systems, typically EFI
(Electronic Fuel Injection), ABS (Anti-block
Braking System), SRS (Air Bag), TC (Traction
Control), AT (Automatic Transmission), etc., are
computerized. Computerization makes the
control precisely, quickly, effectively and safely.
Consequently, a significant progress in vehicle
driveability, fuel economy, power performance,
comfortability, emissions, safety and so on has
been made.
Composition and Working
Principle of Computer- Control
System
The Computer Control System consists of the
on-board computer, and several related control
devices (sensors, switches, and actuators).
Most on-board computers are located inside the
vehicle behind the dashboard, under the
passenger’s or driver’s seat, or behind the right
kick panel. Some manufacturers may still
position it in the engine compartment. The
sensors, switches, and actuators are devices
such as oxygen sensors, coolant temperature
sensors, throttle position sensors, fuel injectors,
etc., that are located throughout the engine,
and are connected by electrical wiring to the
on-board computer. As an example, the
diagram of engine control system is shown in
Fig 6-1.
Fig 6-1
Sensor
It is a device that converts non-electric variable
into electric signal. More than 50 types of
sensor are used in modern vehicles, most of
which are found in powertrain, chassis control
systems, body control system, safety system,
etc.
According to the physical variables controlled,
sensors are sorted into following types:
temperature sensor, pressure sensor, air flow
sensor, position/angular sensor, gas
concentration sensor, rotary speed sensor,
acceleration sensor, vibration sensor, light
sensor, distance sensor, electrical current
sensor, angular speed sensor, shaft sensor,
liquid level sensor, etc.
The commonly-used sensors in corresponding
control systems of vehicle are:
1) In engine management system: intake air
pressure (or air flow), air/fuel ratio,
crankshaft position, knock, RPM, intake air
temperature, coolant temperature and O
2
sensors.
2) In transmission system: vehicle speed,
throttle position, RPM, A/T output shaft
speed, toque, oil pressure/temperature,
shift position sensors.