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Fault Code Reference

SPN 4752 FMI 31AftertreatmentInducement Risk

Aftertreatment DPF System Time Since Last Active Regeneration - Condition Exists

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Overview

Fault Code

SPN 4752 / FMI 31

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DPF assembly located in the aftertreatment system on the exhaust outlet side of the engine, typically mounted under the cab or along the frame rail depending on vehicle configuration.

Common Symptoms

  • DPF lamp illuminated on dash
  • High exhaust backpressure
  • Reduced fuel economy
  • Exhaust smell or white smoke during passive regen attempts
  • Frequent regen requests
  • Engine derate warning message

Root Causes

  • Extended idle operation preventing passive or active regeneration conditions from being met
  • Low exhaust temperatures due to light load or short trip duty cycles
  • DPF soot load too high inhibiting active regen initiation
  • Faulty or out-of-range DPF differential pressure sensor preventing regen trigger
  • Diesel oxidation catalyst (DOC) degraded or poisoned reducing exotherm capability
  • Fuel doser injector clogged or not functioning preventing active regen fuel delivery
  • DEF or SCR system fault causing ACM to inhibit regen
  • EGR system fault causing elevated soot production and rapid DPF loading
  • Operator or system inhibit conditions (PTO, manual inhibit, high exhaust temp warning) preventing regen

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Derate Behavior

Power Derate

Yes

SCR Inducement Risk

If left unresolved, this fault may trigger SCR inducement — a progressive derate enforced by the ECM to ensure emissions compliance.

Mileage / Regen Notes

SPN 4752 FMI 31 indicates the system has not completed an active regen within the expected time window. Active and passive regen will be inhibited or unable to complete. Continued operation may lead to DPF over-soot condition, engine derate, and eventual shutdown if soot load reaches critical threshold.

System Interactions

SPN 4752 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.

Deep-dive diagnostic page: SPN 4752 FMI 31 — 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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