General System

System Description:

The Engine Control Unit (ECU) is the central component of this computerized fuel, ignition and emission control system. Mazda refers to the system as Electronic Gasoline Injection (EGI). To maintain fuel economy, good driveability and reduced vehicle emissions, the ECU monitors data from various sensors and controls functions such as the fuel injection system (air/fuel ratio), ignition system, emission control devices and on-board diagnostics.

The ECU is a computer that judges air/fuel ratio as rich or lean according to a voltage signal generated by an oxygen sensor. Based on oxygen sensor and other input data, the ECU generates a controlling signal to the fuel injectors that regulates "ON" time. Because fuel pressure remains constant, the ECU controls air/fuel ratio adjustments by varying injector "ON" time.

To provide a margin of safety by maintaining driveability in the event of certain system failures, the ECU has a fail-safe mode of preprogrammed values. The output of the ECU will automatically switch to fail-safe mode if a fault is detected in these monitored components and/or systems:

Ignition coil
Crank angle sensor
Airflow meter
Water thermosensor
Intake air thermosensor
Throttle sensor
Pressure sensor
Atmospheric pressure sensor
Oxygen sensor
Feedback system
Metering oil pump system
Knock sensor

The EGI system incorporates self-diagnostic capability monitored via a dash mounted malfunction indicator lamp (MIL). When the system detects a fault in a monitored component and/or circuit, the lamp will light ("CHECK") and stay on (while the engine is running), alerting the driver to seek service. The technician can then extract trouble codes from the ECU to aid in the performance of efficient troubleshooting and repair.

Components can be grouped as ECU input and output devices. Input devices control or produce voltage signals monitored by the ECU. Output devices are components controlled by the ECU. Not all of these devices are monitored by the on-board diagnostic system.

INPUT DEVICES

A/C switch
Airflow meter (code 08)
Atmospheric pressure sensor (code 14)
Back-up light and 5th switch
Clutch and neutral switches
Crank angle sensor
-Ne signal (code 02)
-G signal (code 03)
Electrical load
-Headlight switch
-Blower switch
-Rear defroster switch
-Fog light switch
Feedback system (code 17)
Heat hazard sensor
Ignition coil (trailing side, code 01)
Ignition switch (cranking signal)
Intake air thermosensor
-Air flow meter (code 10)
-Engine (code 11)
Knock sensor (code 05)
Main relay
Metering oil pump position sensor (code 20)
Metering oil pump control system (code 27)
Metering oil pump voltage drop (code 37)
Mileage sensor (#1 and #2)
Oxygen sensor (code 15)
Power steering pressure switch
Pressure sensor (code 13)
Test connector
Throttle sensor
-Full range (code 12)
-Narrow range (code 18)
Water thermosensor (code 09)

OUTPUT DEVICES

A/C relay
AWS and ASV solenoid valves (code 38) [1]
Bypass air control solenoid valve (code 34)
Circuit opening relay
Front secondary injector (code 71)
Fuel injectors/injection timing
Fuel pump resistor relay (code 51)
Igniter (trailing ignition timing)
Igniter (leading ignition timing)
Malfunction indicator lamp (MIL)
Metering oil pump stepping motor (code 26)
Pressure regulator solenoid valve (code 25)
Rear secondary injector (code 73)
Relief solenoid valve (air injection, code 31)
Split air solenoid valve (code 30)
Switch solenoid valve (air injection, code 32)
Wastegate control duty solenoid (code 42)

[1] Accelerated warm-up system and air supply valve