The ECU - Electronic Control Unit on the 1996–1999 Nissan Altima (excluding California-emission 1996 models) is the central controller for the KA24DE 2.4-litre DOHC inline-four engine running Nissan’s ECCS (Electronic Concentrated Control System) multi-point sequential fuel injection. From the 1996 model year onwards the Altima is fully OBD-II compliant, with a standardised 16-pin data link connector for diagnostic access alongside the engine management ECM. The ECM connector carries analogue sensor inputs for throttle position, mass air flow, intake air temperature, engine coolant temperature, and front/rear oxygen sensors, together with injector drive outputs for all four cylinders and dedicated power and sensor ground circuits.
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 connector shown is for 1996–1999 US-market Altima models; 1996 California-emission vehicles use a different ECM calibration and are excluded from this pinout. The ECM is located behind the passenger-side kick panel. OBD-II diagnostic codes are retrieved via the standard 16-pin DLC; the ECM also supports Nissan’s proprietary CONSULT serial interface.
Signals
- Tachometer Signal — engine speed output from the ECM to the instrument cluster tachometer, derived from crankshaft position sensor data
- Throttle Position Sensor — analogue voltage proportional to throttle plate angle; used for load calculation and tip-in enrichment
- Vehicle Speed Sensor — pulse signal indicating road speed, used for idle-up control and speed-density corrections
- Intake Air Temperature Sensor — analogue voltage representing inlet air temperature; used to correct injector pulse width for air density
- O2 Sensor Signal (Front) — narrowband oxygen sensor upstream of the catalytic converter; primary closed-loop fuel control input
- O2 Sensor Signal (Rear) — narrowband oxygen sensor downstream of the catalytic converter; used for catalyst efficiency monitoring under OBD-II
- Mass Air Flow Sensor — analogue voltage from the hot-wire MAF sensor; primary load input for fuel and ignition calculations
- Mass Air Flow Sensor Ground — dedicated ground return for the MAF sensor
- Sensor Ground — common signal-level ground reference for analogue sensor inputs
- Engine Coolant Temperature Sensor — analogue voltage representing coolant temperature; used for cold-start enrichment, idle speed, and fan control
- Injector #1 / #2 / #3 / #4 — low-side drive signals from the ECM to each fuel injector solenoid; pulse width determines fuel quantity
- Power Ground (Electronic Concentrated Control System) — main power ground for the ECM; connects directly to chassis earth