SPN 3719 FMI 4AftertreatmentMedium
DPF Soot Load Sensor - Voltage Low
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Overview
Fault Code
SPN 3719 / FMI 4
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: DPF soot load sensor is mounted on or near the diesel particulate filter housing in the aftertreatment system, typically mid to rear chassis on the exhaust aftertreatment assembly.
Common Symptoms
- Active fault code SPN 3719 FMI 4 logged in aftertreatment module
- DPF soot load reading at or near zero or implausibly low
- Inhibited or forced DPF regeneration cycle
- MIL or aftertreatment warning lamp illuminated
- Inaccurate soot load percentage displayed in diagnostic tool
Root Causes
- Shorted signal wire to ground (low voltage condition) Damaged or corroded sensor connector at DPF soot load sensor Failed DPF soot load sensor (internal short) Chafed or pinched wiring harness causing short to ground Open or high-resistance in sensor supply voltage circuit Moisture intrusion into sensor connector causing short Faulty aftertreatment control module (rare)
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
DPF regeneration is typically inhibited or forced to a fixed interval when SPN 3719 FMI 4 is active, as the ECM cannot accurately determine soot load; some platforms may trigger an immediate forced regen or disable active regen entirely depending on calibration.
System Interactions
SPN 3719 FMI 4 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
TSB Reference: Soot sensor TSB
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 3719 FMI 4 — 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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