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Fault Code Reference

SPN 3563 FMI 31AftertreatmentInducement Risk

Aftertreatment 1 DEF Dosing Valve - Condition Exists

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Overview

Fault Code

SPN 3563 / FMI 31

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DEF dosing valve is typically mounted on the DEF supply line at the inlet to the SCR decomposition tube, near the exhaust mid-pipe or SCR inlet.

Common Symptoms

  • DEF dosing valve not responding to commands
  • Poor NOx conversion efficiency
  • SCR performance fault codes present
  • DEF consumption higher or lower than expected
  • Ammonia slip detected
  • Check engine light illuminated

Root Causes

  • DEF dosing valve clogged or crystallized due to urea deposit buildup DEF dosing valve stuck open or closed DEF supply line restriction or blockage upstream of dosing valve DEF quality issue causing crystallization within valve body Failed or degraded DEF dosing valve solenoid ACM/SCR controller detected dosing valve functional fault during operation or purge cycle DEF pump not delivering adequate pressure to dosing valve Wiring harness chafing or connector corrosion at dosing valve DEF tank empty or low causing air ingestion into dosing system

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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 3563 FMI 31 may inhibit or severely limit DEF dosing, causing SCR system to operate outside target conversion efficiency. Active DPF regeneration may be inhibited if the ACM detects dosing system compromise. Continued operation without dosing can trigger SCR derate and enforce engine power reduction.

System Interactions

SPN 3563 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 3563 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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