Mitsubishi 4m51 Ecu Pinout Work Jun 2026

| Pin | Signal Name | Type | Function | Voltage / Logic | Notes | |-----|----------------------|------------|-------------------------------------------------------------------------|--------------------------------|-----------------------------------------------------------------------| | A1 | Battery +12V | Power In | Main ECU power (unswitched) | 10.5–14.5V DC | Direct from battery via 15A fuse | | A2 | Ground (Power) | Ground | Power ground for injector drivers | 0V | Connect to engine block | | A3 | Ground (Signal) | Ground | Sensor reference ground | 0V | Must be isolated from A2 | | A4 | TPS Signal | Analog In | Throttle position sensor (variable resistor) | 0.5V (idle) – 4.5V (WOT) | 5V reference from ECU pin B4 | | A5 | Water Temp Sensor | Analog In | Engine coolant temperature for cold advance | 2.5V @ 20°C → 0.5V @ 80°C | NTC thermistor, pull-up inside ECU | | A6 | Boost Pressure | Analog In | Turbocharged variants only (0–5V MAP sensor) | 1.2V (atmo) – 4.3V (max boost) | Not used on NA engines; left open | | A7 | Engine Speed (Ne) | Frequency | Magnetic pickup from injection pump (TDC sensor) | AC sine wave 0.5–50V | Critical for governor feedback | | A8 | Vehicle Speed Sensor | Frequency | Reed switch or hall effect in transmission | 0–12V square wave | Used for idle-up and PTO control | | A9 | Stop Solenoid Ctrl | Output | Fuel cutoff solenoid (pull-in and hold) | 12V (initial), 5V (hold) | PWM controlled; failure causes no-start | | A10 | Cold Advance Device | Output | Timing advance solenoid on injection pump | 0V / 12V (on when coolant <40°C)| Increases idle speed | | A11 | EGR Control | Output | EGR vacuum switching valve (if equipped) | 12V PWM (30–80Hz) | Disabled at WOT or low coolant temp | | A12 | Glow Relay Control | Output | Glow plug relay (negative trigger) | Switched to ground (max 2A) | Glow time: 2–10 sec depending on temp | | A13 | Diagnostic Request | Input | Ground this pin to flash trouble codes via check engine light | 0V active low | 12V pull-up inside ECU | | B14 | Ignition Switch (IG) | Power In | Main relay trigger and ECU wake-up | 12V (key on) | Powers internal logic | | B15 | +5V Sensor Reference | Reference | For TPS, MAP, and coolant temp | 5.0V ±0.1V | Short to ground will damage ECU | | B16 | Injector Driver 1 | High-side | Spill valve control for cylinder #1 (indirect injection) | 60–80V peak, 12V hold | – do not probe without scope | | B17 | Injector Driver 2 | High-side | Cylinder #2 | Same as B16 | Use low-impedance test light only | | B18 | Injector Driver 3 | High-side | Cylinder #3 | Same as B16 | | | B19 | Injector Driver 4 | High-side | Cylinder #4 | Same as B16 | | | B20 | Tachometer Output | Signal Out | 4 pulses per revolution for dash tachometer | 12V square wave | Open collector, requires external pull-up | | B21 | A/C Cut Request | Input | Request to raise idle when A/C compressor engages | 12V (A/C on) | Prevents stalling | | B22 | Check Engine Light | Output | Grounds to illuminate MIL | Switched ground, 200mA max | Flashes diagnostic codes when pin A13 grounded | | B23 | Main Relay Control | Output | Activates main power relay (coil) | Switched ground | 12V present at relay coil when ECU active | | B24 | Idle Validation | Digital In | Idle switch from TPS (closed at 0% throttle) | 0V (idle) / 5V (off idle) | Separate from TPS analog signal | | B25 | Brake Switch | Digital In | Disables cruise control / idle-up | 0V (brake off) / 12V (brake on)| | | B26 | Backup Power (Keep) | Power In | For volatile memory (fault codes, learned trims) | 12V continuous | Draws <5mA; loss resets adaptive values |

: Symptoms like an engine that starts but then immediately dies can have many causes. The official approach is to use the M.U.T.-III scan tool to check for DTCs as the first step. If the engine requires a starting fluid to fire, check the fuel delivery system. mitsubishi 4m51 ecu pinout work