ECU - Electronic Control Unit Connector.
The 1998–1999 Acura 2.3 CL uses an OBD2-compliant Engine Control Module (ECM) that governs the F23A1 2.3-litre DOHC engine’s PGM-FI (Programmed Fuel Injection) system, ignition timing, VTEC solenoid operation, and idle air control. The ECM employs three multi-pin connectors — A, B, and C — consistent with Honda’s late-1990s OBD2 connector architecture shared across the Accord and Integra platforms of the same era. Sensor inputs include MAP, throttle position, engine coolant temperature, intake air temperature, and primary and secondary oxygen sensors; a 16-pin Data Link Connector (DLC) provides OBD2 scan-tool access. The ECM is located in the passenger compartment and requires an idle relearn procedure following any power interruption that clears stored diagnostic trouble codes.
Connector A
| Pin | name | Signal |
|---|---|---|
| A19 | Engine Speed Pulse | RPM |
| A23 | Secondary O2 Sensor | Analog |
| A32 | Brake Switch | Analog |
Connector B
| Pin | name | Signal |
|---|---|---|
| B10 | Power Ground | Ground |
| B12 | VTEC Solenoid Valve | Analog |
Connector C
| Pin | name | Signal |
|---|---|---|
| C10 | VTEC Pressure Switch | Analog |
| C16 | Primary O2 Sensor | Analog |
| C17 | MAP Sensor | Analog 0.32V @ -13.9 PSI 4.84V @ 10.94 PSI |
| C23 | Vehicle Speed Sensor | Speed |
| C25 | Intake Air Temperature Sensor | Analog |
| C26 | Engine Coolant Temperature Sensor | Analog |
| C27 | Throttle Position Sensor | Analog |
Notes
Connectors are read from the wire side (back of the connector), not from the pin face, with the locking tab at the top — this orientation determines the pin numbering sequence. To clear stored DTCs, disconnect the negative battery terminal for 30 seconds or remove the ECM backup fuse; doing so also erases idle-learn data, requiring an idle relearn procedure before normal operation resumes. The OBD2 16-pin DLC is located in the passenger compartment and accepts standard SAE J1962 scan-tool connectors.
Signals
- A19 Engine Speed Pulse — RPM signal output from the ECM, derived from the crankshaft/distributor sensor, used by the instrument cluster and ancillary systems.
- A23 Secondary O2 Sensor — analogue input from the downstream (post-catalyst) heated oxygen sensor; used by the ECM to monitor catalytic converter efficiency.
- A32 Brake Switch — analogue input indicating brake pedal application; used for fuel-cut logic and torque converter lock-up control.
- B10 Power Ground — chassis/power ground reference for the ECM.
- B12 VTEC Solenoid Valve — ECM output that energises the Variable Valve Timing and Lift Electronic Control (VTEC) solenoid, switching cam profiles at the programmed RPM/load threshold.
- C10 VTEC Pressure Switch — analogue input confirming hydraulic oil pressure has reached the level required to engage VTEC; ECM uses this as a feedback signal after commanding the solenoid.
- C16 Primary O2 Sensor — analogue input from the upstream (pre-catalyst) heated oxygen sensor; primary feedback signal for closed-loop fuel trim.
- C17 MAP Sensor — analogue input from the Manifold Absolute Pressure sensor (0.32 V at −13.9 PSI vacuum to 4.84 V at 10.94 PSI); primary engine-load signal for fuel and ignition calculations.
- C23 Vehicle Speed Sensor — speed pulse input from the transmission-mounted VSS; used for idle control, torque converter logic, and instrument cluster.
- C25 Intake Air Temperature Sensor — analogue input used to correct fuel delivery for air-density variations.
- C26 Engine Coolant Temperature Sensor — analogue input for cold-start enrichment, cooling-fan control, and temperature-gauge output.
- C27 Throttle Position Sensor — analogue input (0–5 V) indicating throttle plate angle; used for acceleration enrichment and idle/deceleration fuel cut.