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Fault Code Reference

SPN 3055 FMI 0Aftertreatment

Aftertreatment 1 Diesel Particulate Filter Intake Temperature - Data Valid But Above Normal

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Overview

Fault Code

SPN 3055 / FMI 0

Category

Aftertreatment

Derate Risk

Possible

Regen Inhibit

No

Inducement Risk

No

Component Location: DPF intake temperature sensor is mounted on the inlet cone or inlet pipe of the DPF canister, typically mid-chassis on the driver or passenger side of the vehicle.

Common Symptoms

  • Engine derate or power loss
  • Check engine light illuminated
  • High exhaust temperature warning
  • DPF regeneration frequency increases
  • Reduced fuel economy

Root Causes

  • Excessive DPF soot loading causing elevated regeneration temperatures Active regeneration running too long or too frequently due to failed inhibit/request signals Faulty or drifting DPF intake temperature sensor reporting high values Blocked or restricted DPF causing excessive backpressure and heat buildup Faulty diesel oxidation catalyst (DOC) causing uncontrolled exotherm Incorrect or contaminated diesel exhaust fluid (DEF) reducing SCR efficiency and increasing regen demand Engine running rich due to fueling or turbocharger issues increasing exhaust temperatures Cooling air restriction around aftertreatment system components Failed or stuck open 7th injector (in-cylinder or in-exhaust dosing) delivering excess fuel ACM software or calibration issue causing improper regen temperature targeting

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Derate Behavior

Power Derate

Possible

Mileage / Regen Notes

SPN 3055 FMI 0 indicates DPF intake temperature is above normal operating range. Active regeneration may be inhibited by the ACM to prevent thermal damage to the aftertreatment system. If temperature remains elevated, the system may trigger a derate or shutdown to protect components. Manual or forced regeneration should not be attempted until root cause of elevated temperature is identified and corrected.

System Interactions

SPN 3055 FMI 0 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.

Deep-dive diagnostic page: SPN 3055 FMI 0 — Full FSM Sequence & Repair Steps — includes wiring notes, sensor specs, and gated repair procedures.

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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