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Fault Code Reference

SPN 5443 FMI 31AftertreatmentInducement Risk

Aftertreatment DPF Regeneration Disabled - Condition Exists

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Overview

Fault Code

SPN 5443 / FMI 31

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: ACM (Aftertreatment Control Module) is typically mounted on the vehicle firewall, frame rail, or near the aftertreatment system housing depending on OEM and chassis configuration.

Common Symptoms

  • DPF regeneration will not initiate
  • DPF full warning light illuminated
  • Engine derate due to excessive DPF soot loading
  • Increased exhaust backpressure
  • Request for service regeneration required
  • Reduced fuel economy

Root Causes

  • Active fault codes inhibiting regeneration (e.g., SCR, DEF, EGR, or sensor faults) DPF differential pressure sensor fault or out-of-range reading Exhaust gas temperature sensor fault (upstream or downstream of DPF) Low DEF quality or DEF level triggering regen inhibit SCR system fault or NOx sensor fault disabling regen Engine operating conditions not met (idle inhibit, low load, low exhaust temp) Operator inhibit switch active or regen manually disabled ACM/ECM software fault or calibration mismatch DPF soot load at or near maximum with regen blocked by secondary fault Faulty or stuck-open/closed diesel oxidation catalyst (DOC) degrading regen initiation

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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 5443 FMI 31 directly indicates that DPF regeneration has been disabled by a condition present in the aftertreatment system. Active regen (both auto and parked) is fully inhibited while this code is active. The vehicle may illuminate MIL and aftertreatment warning lamps. Soot load will continue to increase until the inhibit condition is resolved. If soot load reaches maximum threshold, vehicle may enter derate or operator inducement. Root cause of the inhibit condition must be resolved before regen can resume.

System Interactions

SPN 5443 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 5443 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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