The 1996–1998 Nissan 240SX (S14 chassis) uses an Engine Control Module (ECM) governed by Nissan’s ECCS (Electronic Concentrated Control System), which provides sequential multi-point fuel injection and electronic ignition timing for the KA24DE 2.4-litre DOHC inline-four engine. From the 1996 model year, US-market 240SX production is universally OBD-II compliant, requiring a standardised 16-pin Data Link Connector alongside the proprietary multi-pin ECM harness connector. The ECM manages injector drive signals, sensor inputs, and oxygen-sensor feedback for closed-loop fuelling on both the front (upstream) and rear (downstream) heated oxygen sensors fitted in the OBD-II exhaust system.
ECU - Electronic Control Unit Connector.
| Pin | name | Signal |
|---|---|---|
| 3 | Tachometer Signal | RPM |
| 23 | Throttle Position Sensor | Analog |
| 26 | Vehicle Speed Sensor | Speed |
| 28 | Intake Air Temperature Sensor | Analog |
| 46 | O2 Sensor Signal (Front) | Analog |
| 47 | Mass Air Flow Sensor | Analog |
| 48 | Mass Air Flow Sensor Ground | Ground |
| 50 | Sensor Ground | Ground |
| 51 | Engine Coolant Temperature Sensor | Analog |
| 52 | O2 Sensor Signal (Rear) | Analog |
| 102 | Injector # 1 | Speed |
| 104 | Injector # 3 | Speed |
| 107 | Injector # 2 | Speed |
| 109 | Injector # 4 | Speed |
| 118 | Power Ground (Electronic Concentrated Control System) | Ground |
Notes
The 240SX S14 was produced in two OBD generations: early 1995 production retained OBD-I diagnostics (same as the outgoing S13), while later 1995 and all 1996–1998 vehicles are OBD-II. This page covers the OBD-II variant (1996–1998, and late-build 1995). The OBD-II ECM features a revised connector layout compared to the OBD-I S13/early-S14 unit; pin numbering above reflects the OBD-II harness. The ECM is located inside the cabin on the passenger side behind the glovebox. Sensor grounds (pins 48 and 50) are separate from the power ground (pin 118), which is the ECCS system ground returned directly to the engine block.
Signals
- Tachometer Signal — engine speed output from the ECM to the instrument cluster tachometer, derived from crank position sensor data.
- Throttle Position Sensor — analogue voltage proportional to throttle plate angle; used for load calculation, idle detection, and acceleration enrichment.
- Vehicle Speed Sensor — pulse signal from the transmission speed sensor, used for speed-density load correction and idle-up control.
- Intake Air Temperature Sensor — negative-temperature-coefficient thermistor signal; ECM corrects fuelling for inlet air density based on this reading.
- O2 Sensor Signal (Front) — analogue voltage from the upstream (pre-catalyst) heated oxygen sensor; primary closed-loop fuelling feedback signal.
- O2 Sensor Signal (Rear) — analogue voltage from the downstream (post-catalyst) heated oxygen sensor; used by the OBD-II monitor to evaluate catalytic converter efficiency.
- Mass Air Flow Sensor — analogue voltage from the hot-wire MAF sensor measuring intake air mass; primary load signal for the ECCS fuelling calculation.
- Mass Air Flow Sensor Ground — dedicated signal ground for the MAF sensor circuit, kept separate to minimise noise on the air-mass signal.
- Sensor Ground — common reference ground for analogue sensor signals including TPS, IAT, and ECT.
- Engine Coolant Temperature Sensor — negative-temperature-coefficient thermistor signal; used for cold-start enrichment, fan control output, and warm-up ignition timing correction.
- Injector #1 / #2 / #3 / #4 — low-side drive signals from the ECM to the four KA24DE fuel injectors; the ECM switches each injector to ground to open it in sequential firing order.
- Power Ground (ECCS) — main ECM power ground; returns ECM operating current to chassis/engine ground and must have a low-resistance connection for correct ECM operation.