| Pin | Signal Name | Wire Color | Type | Behavior | Notes | | :--- | :--- | :--- | :--- | :--- | :--- | | | Main Relay Control | Blue/Red | Output | Switched ground | Engages when key is ON | | B2 | Injector #1 (Cyl 1) | Blue | High-side drive | Pulse width mod | Do NOT probe with standard LED; use lab scope | | B3 | Injector #2 (Cyl 2) | Blue/Yellow | High-side drive | PWM (Battery voltage) | Very short pulses (~1ms at idle) | | B4 | Injector #3 (Cyl 3) | Blue/Green | High-side drive | PWM | Resistance: ~0.5-1.0 Ohms | | B5 | Injector #4 (Cyl 4) | Blue/Red | High-side drive | PWM | Group injection typically | | B8 | Suction Control Valve (SCV) | White/Red | PWM | 0-100% duty cycle | Controls fuel pressure; ~5-10 Ohms | | B12 | Common Rail Relief Valve | Black/Yellow | Output | Battery voltage | Opens on over-pressure | | B15 | Engine Stop Solenoid | Red/White | Output | Battery voltage | Cuts fuel on key-off | | B18 | Battery +12V (Main) | Thick White | Power | 10-14V | Switched via main relay | | B19 | Ground (Actuators) | Thick Black | Ground | 0V | High-current return for injectors |
A typical 4M51 ECU configuration includes multiple connectors handling various inputs and outputs to the engine's sensors and actuators. mitsubishi 4m51 ecu pinout work