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
SPN 91 FMI 3Throttle position sensor high · CATSPN 91 FMI 3Accelerator pedal position sensor voltage high · DetroitSPN 91 FMI 3Accelerator pedal position sensor voltage high · InternationalSPN 91 FMI 3Accelerator pedal position sensor voltage high · PACCARSPN 91 FMI 3Accelerator pedal position sensor voltage high · MERCEDESSPN 91 FMI 3Accelerator pedal position sensor voltage high · VolvoSPN 91 FMI 3Accelerator pedal position sensor voltage high · MackSPN 91 FMI 3Accelerator pedal position sensor voltage high · CumminsSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · CATSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · DetroitSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · InternationalSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · PACCARSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · MERCEDESSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · VolvoSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · MackSPN 94 FMI 3Fuel delivery pressure sensor circuit voltage above normal · CumminsSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · CATSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · DetroitSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · InternationalSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · PACCARSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · MERCEDESSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · VolvoSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · MackSPN 100 FMI 3Engine oil pressure sensor circuit voltage above normal · Cummins
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