Detailed guide for SPN 3610 FMI 4
Back to top ↑What this fault means
SPN 3610 FMI 4 indicates a low-voltage condition on the applicable DPF or exhaust-pressure sensing circuit. FMI 4 generally means the ECM is seeing voltage below the expected range.
A low electrical signal does not necessarily mean actual exhaust pressure is low. The problem may be in the sensor circuit rather than in the DPF itself.
What you may notice
The truck may display an aftertreatment warning, unusual regeneration behavior or implausible exhaust-pressure readings. Secondary DPF or regeneration codes can appear if the ECM cannot trust the pressure information.
What to check first
Inspect the pressure sensor connector and wiring. Look for open circuits, damaged terminals, rubbed wiring, poor grounds and corrosion.
Verify sensor supply voltage and ground according to the OEM wiring diagram. Check whether the signal changes logically when the engine is running and exhaust flow increases.
Also inspect the pressure plumbing
Where the sensor uses pressure tubes or hoses, inspect them for blockage, damage, condensation or soot buildup. An electrical FMI should be diagnosed electrically first, but a restricted pressure path can create confusing readings and companion faults.
Before replacing the DPF
Do not replace or clean the DPF solely because this SPN is present. First establish whether the ECM is receiving a valid pressure signal.
If the circuit tests correctly but the signal remains abnormal, test or replace the sensor according to the OEM procedure. Verify the exact sensor location and expected voltage range for the specific engine.
Mechanic community notes for SPN 3610 FMI 4
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