SPN 3249 FMI 7AftertreatmentInducement Risk
DEF Pump Motor Speed - Mechanical System Not Responding
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Overview
Fault Code
SPN 3249 / FMI 7
Category
Aftertreatment
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
Yes — SCR inducement possible
Component Location: DEF pump is mounted on the chassis frame rail or exhaust system near the DEF tank.
Common Symptoms
- DEF system malfunction lamp illuminated
- Engine derate or power loss
- DEF dosing disabled or reduced
- Inability to perform DEF pump priming
- SCR system efficiency fault
- DEF pump audible noise absent when commanded
Root Causes
- DEF pump motor seized or mechanically failed (worn brushes, armature failure) DEF crystallization inside the pump causing mechanical blockage Frozen DEF in pump or supply lines restricting/preventing motor rotation DEF pump filter screen clogged with DEF crystals or debris DEF pump supply line kinked, collapsed, or internally obstructed DEF pump pressure relief valve stuck or failed DEF tank suction strainer heavily fouled Incorrect DEF concentration (diluted or contaminated fluid) causing pump inefficiency DEF pump motor drive circuit fault causing under-voltage to motor (masquerading as mechanical fault) ACM software or calibration issue misinterpreting motor speed feedback
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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 7 will inhibit DEF dosing to the SCR catalyst. Without active DEF injection, SCR NOx conversion efficiency drops, which will trigger SCR efficiency faults and may illuminate MIL. Depending on fault severity and OBD trip accumulation, active DPF regeneration may be inhibited if the ACM enters a protective derate mode. Extended operation without DEF dosing will result in inducement derate (engine power and/or speed reduction) per EPA 2010+ guidelines after fault thresholds are exceeded.
System Interactions
SPN 3249 FMI 7 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3249 FMI 7 — 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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