EFI 15A Fuse Blowing Repeatedly - Failed ECU Shorting +B Circuit to Ground

Electricalintermediate✓ OP Confirmed

Problem

The EFI 15 amp fuse blows immediately when the key is turned to the run position. The yellow connector by the fuse box was identified as the circuit where the short occurs. The issue persisted even with the fuel pump, fuel pump relay, and O2 sensor disconnected.

EFI 15A fuse blows instantly when key is turned to run positionFuse does not blow with key offFuse still blows with fuel pump disconnectedFuse still blows with fuel pump relay disconnectedFuse still blows with O2 sensor disconnectedBlack/Red (+B) wire shows 0 ohms to ground with ECU plugged in

Root Cause

The ECU had an internal failure, likely in the 5V regulator transistor or protection diodes on the +B circuit. This caused the Black/Red (+B) wire to short directly to ground through the ECU, blowing the EFI 15A fuse as soon as the ignition was turned on.

Confidence

High confidence — Original poster confirmed this resolved the issue

View Original Thread →Posted July 2022 on SupraForums.com