SPN 3471 FMI 16Aftertreatment
Aftertreatment 1 Diesel Exhaust Fluid Tank Temperature 1 - Data Valid But Above Normal
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Overview
Fault Code
SPN 3471 / FMI 16
Category
Aftertreatment
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: DEF tank temperature sensor is mounted on or integrated into the DEF tank assembly, typically located on the chassis frame rail or under cab near the DEF supply module.
Common Symptoms
- DEF temperature warning lamp illuminated
- DEF system malfunction indicator active
- Reduced DEF dosing or injection disabled
- Engine derate warning displayed
- DEF consumption appears abnormal
- SCR efficiency reduced
Root Causes
- DEF tank fluid temperature genuinely elevated due to high ambient temps or hot exhaust proximity Faulty or out-of-calibration DEF tank temperature sensor reading high DEF tank heating element stuck ON or shorted, causing excessive fluid heating Poor ground connection at DEF tank sensor or module connector causing erroneous high reading Damaged or corroded wiring harness near DEF tank causing signal offset ACM software or calibration issue misinterpreting sensor signal DEF tank coolant return line restriction causing heat buildup in tank
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Derate Behavior
Power Derate
No
Mileage / Regen Notes
SPN 3471 FMI 16 can inhibit or suspend active DPF regeneration when DEF tank temperature exceeds safe operating thresholds, as the ACM may limit DEF dosing to protect fluid integrity; prolonged high DEF temps risk urea decomposition and injector crystallization.
System Interactions
SPN 3471 FMI 16 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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3471 FMI 16 — 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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