The 1996–2001 Honda Prelude (BB6 chassis) uses Honda’s PGM-FI Engine Control Module (ECM) to manage fuel injection, ignition timing, and the VTEC variable valve-timing system on the H22A4 2.2-litre DOHC VTEC engine. From 1996, the Prelude moved to OBD2 compliance, adding a 16-pin Data Link Connector for diagnostic scan tools. The ECM uses three lettered connectors — A, C, and D — and is mounted in the passenger-compartment kick panel area. The terminal arrangement is read from the wire side of each connector with the locking tab at the top.
ECU - Electronic Control Unit Connector.
Connector A
| Pin | name | Signal |
|---|---|---|
| A8 | VTEC Solenoid Valve | Analog |
| A10 | Power Ground | Ground |
| A20 | Ignition Control Module | RPM |
| A23 | Power Ground | Ground |
Connector C
| Pin | name | Signal |
|---|---|---|
| C15 | VTEC Pressure Switch | Analog |
| C18 | Vehicle Speed Sensor | Speed |
Connector D
| Pin | name | Signal |
|---|---|---|
| D1 | Throttle Position Sensor | Analog |
| D2 | Engine Coolant Temperature Sensor | Analog |
| D3 | MAP Sensor | Analog 0.32V @ -13.9 PSI 4.84V @ 10.94 PSI |
| D5 | Brake Switch | Analog |
| D7 | Primary O2 Sensor | Analog |
| D8 | Intake Air Temperature Sensor | Analog |
| D14 | Secondary O2 Sensor | Analog |
Notes
Connectors are read from the wire side (back of the connector), not the pin face, with the locking tab oriented upward. The ECM resets stored diagnostic trouble codes when the negative battery terminal is disconnected for at least 30 seconds, or when the ECM backup fuse is removed; this also clears idle learn data, requiring an idle relearn procedure. The OBD2 16-pin DLC is located in the cabin for scan tool or Honda PGM Tester access.
Signals
Connector A
- A8 — VTEC Solenoid Valve — ECM-driven output that energises the VTEC oil-pressure solenoid to switch cam-lobe profiles on the H22A4 at the programmed engine speed and load threshold.
- A10 — Power Ground — chassis/power ground reference for the ECM.
- A20 — Ignition Control Module — RPM signal path between the ECM and the ignition control module; used by the ECM to control ignition timing.
- A23 — Power Ground — second chassis/power ground reference for the ECM.
Connector C
- C15 — VTEC Pressure Switch — input from the VTEC oil-pressure switch confirming that hydraulic pressure has been established in the VTEC system after the solenoid is energised.
- C18 — Vehicle Speed Sensor — pulse signal from the vehicle speed sensor used by the ECM to monitor road speed.
Connector D
- D1 — Throttle Position Sensor — analogue voltage input indicating throttle-plate angle; used by the ECM for fuel and ignition calculations.
- D2 — Engine Coolant Temperature Sensor — analogue input from the ECT sensor; ECM uses coolant temperature for cold-start enrichment and fan control.
- D3 — MAP Sensor — manifold absolute pressure signal (0.32 V at −13.9 PSI to 4.84 V at 10.94 PSI); primary engine load input for PGM-FI fuel calculations.
- D5 — Brake Switch — input indicating brake-pedal application; used by the ECM for idle-speed control logic.
- D7 — Primary O2 Sensor — upstream heated oxygen sensor signal; ECM uses this for closed-loop fuel trim.
- D8 — Intake Air Temperature Sensor — analogue input from the IAT sensor; ECM uses inlet-air temperature to correct fuel delivery.
- D14 — Secondary O2 Sensor — downstream oxygen sensor signal used by the ECM for catalyst-efficiency monitoring.