ECU - Electronic Control Unit Connector.
The 1996 and 1997 Mazda Miata (NA chassis) introduced an updated Engine Control Module (ECM) to meet OBD-II requirements — making the 1996 model year the first Miata with a fully OBD-II compliant engine management system. The unit manages the BP-ZE 1.8 L four-cylinder engine and is located behind the right seat rather than the kick panel used on earlier NA models. Two OBD-II data-link connectors are fitted: a primary DLC on the left side of the engine compartment and a secondary DLC-2 below the centre of the dashboard. Mazda colour codes in wiring diagrams follow the convention B = Black, W = White, R = Red, G = Green, Y = Yellow, L = Blue, Lg = Light Green.
Connector 1
| Pin | name | Signal |
|---|---|---|
| 1M | Vehicle Speed Sensor | Speed |
| 1O | Power Ground | Ground |
| 1Q | Brake Switch | Analog |
Connector 3
| Pin | name | Signal |
|---|---|---|
| 3B | Mass Air Flow | Analog |
| 3C | Primary O2 Sensor | Analog |
| 3D | Secondary O2 Sensor | Analog |
| 3F | Throttle Position Sensor | Analog |
| 3G | Engine Coolant Temperature Sensor | Analog |
| 3K | Intake Air Temperature Sensor | Analog |
Connector 4
| Pin | name | Signal |
|---|---|---|
| 4A | Power Ground | Ground |
| 4L | Tachometer Output | RPM |
Notes
The ECM is mounted behind the right seat; earlier 1990–1995 NA Miata units were located at the driver-side kick panel. The 1996 redesign added a second connector to accommodate the additional OBD-II monitoring circuits. Sample terminal IDs confirmed in the factory supplement include 1D (WHT/BLK), 4B (WHT/RED), 4L (BLK/WHT), 1I (LT GRN/YEL), 1U (LT GRN), and 1A (BLK/GRN).
Signals
- Vehicle Speed Sensor — pulse signal from the transmission speed sensor; used by the ECM for fuel and idle control calculations.
- Power Ground — chassis/power earth reference for the ECM.
- Brake Switch — indicates brake pedal application; used for idle-up control and cruise-cancel logic.
- Mass Air Flow — analogue voltage from the MAF (airflow meter) indicating inducted air mass.
- Primary O2 Sensor — upstream (pre-catalytic converter) heated oxygen sensor signal; used for closed-loop fuelling.
- Secondary O2 Sensor — downstream (post-catalytic converter) oxygen sensor signal; monitors catalytic converter efficiency for OBD-II.
- Throttle Position Sensor — analogue voltage proportional to throttle blade angle.
- Engine Coolant Temperature Sensor — thermistor signal for coolant temperature; used for cold-start enrichment and fan control.
- Intake Air Temperature Sensor — thermistor signal for inlet air temperature; used to correct fuel delivery.
- Tachometer Output — engine speed pulse signal (RPM) routed to the instrument cluster.