FMI 3 — Voltage above normal or shorted to high source
The signal wire is seeing more voltage than the circuit should ever produce — usually the signal wire touching battery power or the 5 V reference.
Common causes
- Signal wire shorted to a power or reference wire
- Chafe at a bracket, clamp or through a frame pass-through
- Water or coolant in the connector bridging pins
- Failed sensor shorting internally
What to test, in order
- Unplug the sensor and read the signal pin — a live reading with the sensor unplugged proves the short is in the harness
- Check for battery voltage on the signal circuit key-on
- Inspect the connector for moisture and corrosion, dry it and retest
- Compare against a known-good sensor before replacing the harness
Codes we document with FMI 3
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