Komatsu Fault Code

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SPN 3509 FMI 4

All Digging Telemetry Lost on Monitor

System

Electrical

Symptom

All Digging Telemetry Lost on Monitor

Diagnosis & fix steps

LOGIC: Sensor Supply 5V Reference 1 Circuit Low (Shorted to Ground). ACTION: Unplug shared 5V line sensors (MAP, rail pressure, oil temp) one by one until global 5V reference recovers on scan tool to isolate shorted transducer.

Red Seal field insights

Shared Rail Trap: An internal short to ground inside a single sensor collapses the entire shared 5V supply line array, blinding adjacent sensors simultaneously.

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