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Fault Code Reference

SPN 3719 FMI 2AftertreatmentInducement Risk

Aftertreatment 1 Diesel Exhaust Fluid Tank Temperature 1 - Data Erratic, Intermittent, or Incorrect

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Overview

Fault Code

SPN 3719 / FMI 2

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: DEF tank temperature sensor is located at or within the DEF tank assembly, typically on the underside or side of the vehicle's DEF tank, often integrated into the DEF pump/level/temp module.

Common Symptoms

  • DEF quality fault codes present
  • DEF tank temperature reading fluctuating or unrealistic
  • SCR system efficiency faults may accompany
  • Amber warning lamp illuminated
  • DEF consumption rate inaccurate or abnormal
  • DEF system derates counting down

Root Causes

  • Faulty or degraded DEF tank temperature sensor Corroded or damaged sensor connector/harness at the DEF tank Water intrusion into the DEF tank temperature sensor connector Intermittent open or short in the wiring harness between DEF tank sensor and ACM DEF tank contamination affecting sensor accuracy Failed DEF pump/supply module assembly (on integrated sensor designs) ACM software or calibration issue causing erratic signal interpretation Poor ground connection at DEF tank module or ACM

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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

An erratic DEF tank temperature signal may inhibit active DPF regeneration if the ACM cannot confirm DEF system readiness. Regeneration may be delayed or inhibited to protect the SCR system from dosing errors.

System Interactions

SPN 3719 FMI 2 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 3719 FMI 2 — 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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