What are the symptoms of SPN 3480 FMI 2?

MIL or Check Engine light illuminated. DEF dosing reduced or disabled. Erratic DPF pressure readings on scan tool. Frequent or failed parked regenerations. Poor engine performance or hesitation. Excessive fuel consumption during regen attempts

What causes SPN 3480 FMI 2?

Plugged or kinked DPF differential pressure sensor signal hoses (most common). DPF differential pressure sensor ports clogged with soot or moisture. Faulty or degraded DPF differential pressure sensor. Loose or corroded connector at the DPF differential pressure sensor. Chafed, open, or shorted signal wire between sensor and ACM. Cracked or disconnected pressure hose fittings at DPF inlet tap. ACM software anomaly or calibration mismatch. Failed or damaged DPF causing abnormal pressure differential readings. Water intrusion into sensor or connector

How do I diagnose SPN 3480 FMI 2?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 3480 FMI 2 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 3480 FMI 2Aftertreatment

Aftertreatment 1 Diesel Particulate Filter Intake Pressure - Data Erratic, Intermittent, or Incorrect

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Overview

Fault Code

SPN 3480 / FMI 2

Common Symptoms

MIL or Check Engine light illuminated
DEF dosing reduced or disabled
Erratic DPF pressure readings on scan tool
Frequent or failed parked regenerations
Poor engine performance or hesitation
Excessive fuel consumption during regen attempts

Root Causes

Plugged or kinked DPF differential pressure sensor signal hoses (most common)
DPF differential pressure sensor ports clogged with soot or moisture
Faulty or degraded DPF differential pressure sensor
Loose or corroded connector at the DPF differential pressure sensor
Chafed, open, or shorted signal wire between sensor and ACM
Cracked or disconnected pressure hose fittings at DPF inlet tap
ACM software anomaly or calibration mismatch
Failed or damaged DPF causing abnormal pressure differential readings
Water intrusion into sensor or connector

Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.

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Derate Behavior

Power Derate

Yes

Mileage / Regen Notes

An erratic or incorrect DPF intake pressure signal (FMI 2) will typically inhibit active DPF regeneration since the ACM cannot accurately determine soot load or DPF restriction level. Forced or parked regen requests may be blocked until fault is resolved.

System Interactions

SPN 3480 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.

DPF differential pressure monitoring — soot load calculations affected

SCR NOx conversion efficiency — DEF dosing strategy may be altered

Active regen inhibit logic — regen may be blocked or delayed

Engine protection derate — ECM may reduce power to protect components

Common Diagnostic Mistakes

Replacing the sensor without verifying wiring continuity and supply voltage first.

Clearing codes without identifying and resolving the root cause — the fault will return.

Ignoring related active faults — cascading faults often share a root cause.

Skipping the connector inspection — corrosion and damaged pins are a leading cause of sensor faults.

Condemning the ECM before exhausting all wiring and component tests.

Replacing the DPF without verifying the regen system is functional — a failed regen injector will reload the new DPF.

Ignoring DEF quality — contaminated DEF causes SCR efficiency faults that look like hardware failures.

Related Faults in This Category

SPN 5246-31SCR NOx Efficiency Low SPN 4364-18DEF Dosing Below Normal SPN 3364-2DEF Quality Erratic SPN 3251-0DPF Differential Pressure High SPN 3719-16DPF Soot Load High

OEM System Resources

Cummins Fault Codes Detroit Diesel Fault Codes PACCAR Fault Codes Volvo Fault Codes Freightliner Fault Codes Mack Fault Codes

ASE Training Resources

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Authority References

Diagnostic procedures on this page are informed by OEM service literature and industry standards.

EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.Cummins QuickServe OnlineOfficial Cummins service manuals, fault code lookup, and TSB database.Detroit Diesel DiagnoCentralDetroit Diesel diagnostic procedures, DDDL documentation, and service literature.PACCAR MX Engine ServicePACCAR MX-11 and MX-13 engine service documentation and DAVIE diagnostic guides.Volvo/Mack Tech ToolVolvo and Mack engine fault code reference and PTT/Tech Tool diagnostic procedures.ASE — Diesel Truck Technician CertificationNational Institute for Automotive Service Excellence — T2 Diesel Engines certification standards.

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