Detailed guide for SPN 3480 FMI 4
Back to top ↑What SPN 3480 FMI 4 means
SPN 3480 FMI 4 is documented on Detroit applications as a fuel compensation pressure sensor circuit failed-low condition.
FMI 4 indicates voltage below normal or a signal shorted toward a low source.
What you may notice
The malfunction indicator lamp or check-engine light may illuminate.
The reported aftertreatment fuel pressure may appear too low or invalid because of an electrical circuit problem.
What to check first
Inspect the fuel compensation pressure sensor connector and wiring for corrosion, damaged terminals, shorts to ground or open circuits.
Check for related SPN 4077 or other aftertreatment fuel-pressure circuit faults.
Use the OEM wiring diagram to verify sensor supply, ground and signal circuits.
Before replacing the sensor
Do not replace the sensor solely because FMI 4 is active. Wiring faults can create the same low-voltage condition.
Confirm the circuit and sensor using the manufacturer's diagnostic procedure.
Mechanic community notes for SPN 3480 FMI 4
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