Isuzu 4hl1-1 Ecu Pinout -

| Pin | Function | Wire Color (Typical) | Voltage/Logic | | :--- | :--- | :--- | :--- | | | Main Battery Positive (ECU Backup) | White/Red | 12V Constant | | A-2 | Main Battery Positive (Injector Driver) | White/Red | 12V Constant | | A-10 | Main Ground (Power stage) | Black/White | 0V | | A-11 | Main Ground (Power stage) | Black | 0V | | A-20 | Ignition Switch (IG SW) | Black/Yellow | 12V (Key ON) | | A-22 | Main Relay Control (ECU grounds to activate) | Light Green | Signal to relay coil |

If the engine cranks but does not start, check pin A23 (signal): isuzu 4hl1-1 ecu pinout

For a complete, vehicle-specific pinout with wire colors, buy the 30-minute access to (Dealer service info) or download a genuine Isuzu NPR Workshop Manual for your year. It will save you days of headaches. | Pin | Function | Wire Color (Typical)

If you want, I can:

The Suction Control Valve (pins A09, A10) is a common failure point. At idle, duty cycle is ~25–30%. You’ll see average voltage on A09 of ~3–4V relative to ground, but this is PWM. A test light will flicker. A multimeter in DC mode gives only an average reading. At idle, duty cycle is ~25–30%