ECU - Electronic Control Unit Connector.
The NA-chassis Mazda Miata (MX-5) produced from 1990 to 1995 uses a Mitsubishi-designed EGI (Electronic Gasoline Injection) Engine Control Unit to manage fuelling, ignition, and emissions functions. The 1990–1993 models are fitted with the 1.6 L B6-ZE four-cylinder, whilst 1994–1995 cars use the 1.8 L BP-ZE; both share the same ECU connector family, designated CONN #1 and CONN #2 in the factory wiring diagrams. The unit is located at component grid 2 (A 4–7) and is labelled “ENGINE CONTROL UNIT (ECU)” in the factory wiring documentation. Controlled signals include the oxygen sensor, idle speed control solenoid, fuel injectors, crank angle sensor, coolant thermal sensor, airflow meter, throttle position sensor, A/C relay, coolant fan relay, tachometer output, and the diagnosis connector.
Connector 1
| Pin | name | Signal |
|---|---|---|
| 1O | Brake Switch | Analog |
Connector 2
| Pin | name | Signal |
|---|---|---|
| 2B | Power Ground | Ground |
| 2I | Tachometer Output | RPM |
| 2M | Throttle Position Sensor | Analog |
| 2N | Primary O2 Sensor | Analog |
| 2O | Mass Air Flow | Analog |
| 2P | Intake Air Temperature Sensor | Analog |
| 2Q | Engine Coolant Temperature Sensor | Analog |
Signals
- Brake Switch — signals the ECU when the brake pedal is depressed; used for idle-up and torque-converter control on automatic-transmission variants.
- Power Ground — chassis/power ground reference for the ECU.
- Tachometer Output — pulse signal to the instrument-cluster tachometer, derived from the ignition circuit.
- Throttle Position Sensor — analogue voltage indicating throttle plate angle; separate calibrations exist for manual and automatic transmission variants.
- Primary O2 Sensor — voltage signal from the upstream exhaust oxygen sensor; used by the ECU for closed-loop fuel correction.
- Mass Air Flow — analogue signal from the airflow meter (vane-type on NA Miata) indicating inducted air volume.
- Intake Air Temperature Sensor — analogue voltage from the IAT sensor, typically integrated into the airflow meter housing on the B6-ZE.
- Engine Coolant Temperature Sensor — analogue voltage from the coolant thermal sensor; governs cold-start enrichment, fan relay, and idle-speed control.
Notes
The ECU uses two multi-pin connectors (CONN #1 and CONN #2) as shown in the factory engine-control wiring diagram. The 1990–1993 cars with the B6-ZE engine share the same ECU connector family as the 1994–1995 BP-ZE cars; however, automatic-transmission models have additional terminals for the throttle position sensor calibration and A/T-specific signals. The ECU is not OBD-II compliant; that requirement was introduced on the 1996 model year Miata. Factory wiring diagrams use Mazda colour codes: B = Black, W = White, R = Red, G = Green, Y = Yellow, L = Blue, O = Orange, Lg = Light green.