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Fault Code Reference

SPN 5827 FMI 31AftertreatmentInducement Risk

Aftertreatment 1 Diesel Exhaust Fluid Quality Poor

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Overview

Fault Code

SPN 5827 / FMI 31

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DEF quality sensor is located inside or on the DEF tank, typically mounted on the DEF tank module assembly, accessible from under the vehicle or chassis rail.

Common Symptoms

  • DEF quality poor warning light illuminated
  • DEF consumption higher than normal
  • Inducement countdown timer active
  • Poor NOx conversion efficiency
  • Repeated SPN 5827 FMI 31 fault codes
  • SCR system performance degraded
  • MIL or amber warning lamp illuminated

Root Causes

  • Non-compliant or contaminated DEF fluid (e.g., water, diesel, or incorrect urea concentration)
  • DEF concentration below ISO 22241 standard (should be 32.5% urea)
  • DEF tank filled with wrong fluid (diesel, coolant, or water)
  • Faulty or degraded DEF quality sensor giving false readings
  • DEF quality sensor connector corrosion or poor electrical connection
  • DEF that has been frozen and improperly thawed, altering concentration
  • Aged or expired DEF that has degraded beyond acceptable limits
  • DEF quality sensor contaminated with debris or crystallized urea

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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

Active and parked DPF regeneration will be inhibited when DEF quality is flagged as poor. SCR efficiency is compromised, leading to potential NOx non-compliance. Extended poor DEF quality conditions may trigger derate (torque/speed reduction) and operator warning lamp. Regen will remain inhibited until DEF quality fault is resolved and cleared.

System Interactions

SPN 5827 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 5827 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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