: Manual diagnostics through display codes without a scan tool.
Many Google Images results show a simple table like “Pin 1 – 12V, Pin 2 – GND” – that’s dangerous. The 4HL1 ECU has . Missing a single shield ground or sensor return can burn the ECU driver IC. isuzu 4hl1 ecu pinout link
The light blue wire—the crank signal wire—had corroded right at the splice. The ECU was blind. It didn't know the engine was turning over, so it didn't fire the injectors. : Manual diagnostics through display codes without a