Equus 3110 - CanOBD2 Diagnostic Tool - Manual (Page 17)

CAN OBD2 15
E
Onboard Diagnostics
COMPUTER ENGINE CONTROLS
The Basic Engine Computer Control System
The on-board computer is the heart of the Computer
Control System. The computer contains several programs
with preset reference values for air/fuel ratio, spark or igni-
tion timing, injector pulse width, engine speed, etc.
Separate values are provided for various driving conditions,
such as idle, low speed driving, high-speed driving, low load,
or high load. The preset reference values represent the ideal
air/fuel mixture, spark timing, transmission gear selection,
etc., for any driving condition. These values are programmed
by the vehicle manufacturer, and are specific to each vehicle model.
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. However, some manufacturers may still position it in the
engine compartment.
Vehicle sensors, switches, and actuators are located throughout the
engine, and are connected by electrical wiring to the on-board
computer. These devices include oxygen sensors, coolant tempera-
ture sensors, throttle position sensors, fuel injectors, etc. Sensors and
switches are input devices. They provide signals representing current
engine operating conditions to the computer. Actuators are output
devices. They perform actions in response to commands received
from the computer.
The on-board computer receives information inputs from sensors and
switches located throughout the engine. These devices monitor critical
engine conditions such as coolant temperature, engine speed, engine
load, throttle position, air/fuel ratio etc.
The Computer Control System consists of an on-board
computer and several related control devices (sensors,
switches, and actuators).
OUTPUT DEVICES
Fuel Injectors
Idle Air Control
EGR Valve
Ignition Module
On-Board
Computer
INPUT DEVICES
Coolant Temperature Sensor
Throttle Position Sensor
Fuel Injectors
INPUT DEVICES
Oxygen Sensors
TYPICAL COMPUTER
CONTROL SYSTEM