SPN 4374 FMI 6AftertreatmentMedium
DEF Dosing Valve - Current Above Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 4374 / FMI 6
Category
Aftertreatment
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: DEF dosing valve mounted on the SCR mixer pipe or decomposition tube, typically on the exhaust mid-pipe between the DPF and SCR catalyst.
Common Symptoms
- Erratic DEF dosing, possible over-dosing
Root Causes
- DEF dosing valve coil shorted internally causing excessive current draw Wiring harness short to ground on the DEF dosing valve control circuit Chafed or damaged wiring between the DCU/ACM and the DEF dosing valve Failed or stuck-open DEF dosing valve with internal coil damage Moisture or DEF fluid contamination inside the dosing valve connector causing a short Failed Dosing Control Unit (DCU) or Aftertreatment Control Module (ACM) output driver shorted Corroded or damaged DEF dosing valve connector pins causing intermittent short to ground DEF crystallization bridging connector terminals causing current path to ground
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
Short circuit — inspect wiring before replacing valve.
System Interactions
SPN 4374 FMI 6 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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4374 FMI 6 — 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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