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Fault Code Reference

SPN 3249 FMI 9AftertreatmentInducement Risk

DEF Pump Motor Speed - Abnormal Update Rate

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Overview

Fault Code

SPN 3249 / FMI 9

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DEF pump motor is located at the DEF pump assembly, typically mounted near the DEF tank or frame rail, connected to ACM via dedicated CAN harness.

Common Symptoms

  • Check engine light or malfunction indicator lamp illuminated
  • DEF system warning message on instrument cluster
  • Reduced engine power or derate condition
  • DEF pump inoperative or intermittent operation
  • SCR system efficiency reduced or inactive
  • Increased NOx emissions

Root Causes

  • Loss of CAN communication between ACM and DEF pump motor controller module Damaged, corroded, or loose CAN bus wiring or connectors at DEF pump harness DEF pump motor controller module failure or internal fault Open or short circuit in CAN High/CAN Low wiring between ACM and DEF pump module Missing or incorrect CAN termination resistor (120 ohm) at DEF pump node ACM software or calibration mismatch causing CAN message timeout DEF pump motor controller module not properly powered or grounded Corrupted or absent CAN network address/configuration for DEF pump node

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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 3249 FMI 9 (DEF pump motor speed abnormal update rate) will typically inhibit active DPF regeneration because the ACM cannot confirm proper DEF/SCR system operation. DEF dosing may be suspended, leading to SCR system deactivation. Prolonged absence of DEF dosing can result in elevated NOx emissions and may trigger additional SCR-related fault codes. If the fault is active, forced or parked DPF regeneration may be blocked by the ACM. The vehicle may enter a derate condition depending on OEM-specific SCR fault escalation logic.

System Interactions

SPN 3249 FMI 9 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 3249 FMI 9 — 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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