What are the symptoms of SPN 5578 FMI 31?

High exhaust temperature warning lamp illuminated. Exhaust temperature gauge reading abnormally high. Excessive heat from exhaust system components. Aftertreatment system protection mode active. Reduced engine power or torque limiting. Inability to complete DPF regeneration cycles. Burning smell near exhaust components

What causes SPN 5578 FMI 31?

Excessive unburned fuel entering the aftertreatment system causing exothermic reaction Stuck open or leaking diesel injector causing fuel enrichment Malfunctioning or stuck DEF doser injector contributing to uncontrolled exotherm Failed or out-of-range exhaust temperature sensor providing false high reading Runaway DPF regeneration due to excessive soot load combined with uncontrolled fuel injection ACM software or calibration fault causing improper regen fuel quantity command Blocked or restricted exhaust flow causing heat buildup upstream of DPF Faulty turbocharger allowing excess crankcase oil into exhaust stream

How do I diagnose SPN 5578 FMI 31?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 5578 FMI 31 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 5578 FMI 31Aftertreatment

Aftertreatment 1 Diesel Exhaust System High Temperature

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Overview

Fault Code

SPN 5578 / FMI 31

Common Symptoms

High exhaust temperature warning lamp illuminated
Exhaust temperature gauge reading abnormally high
Excessive heat from exhaust system components
Aftertreatment system protection mode active
Reduced engine power or torque limiting
Inability to complete DPF regeneration cycles
Burning smell near exhaust components

Root Causes

Excessive unburned fuel entering the aftertreatment system causing exothermic reaction Stuck open or leaking diesel injector causing fuel enrichment Malfunctioning or stuck DEF doser injector contributing to uncontrolled exotherm Failed or out-of-range exhaust temperature sensor providing false high reading Runaway DPF regeneration due to excessive soot load combined with uncontrolled fuel injection ACM software or calibration fault causing improper regen fuel quantity command Blocked or restricted exhaust flow causing heat buildup upstream of DPF Faulty turbocharger allowing excess crankcase oil into exhaust stream

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

SPN 5578 FMI 31 will inhibit active DPF regeneration immediately to prevent thermal damage to the aftertreatment system; a high-temperature derate or engine protection shutdown may be commanded depending on OEM calibration thresholds.

System Interactions

SPN 5578 FMI 31 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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