AI Diesel Tech

Fault Code Reference

SPN 4374 FMI 19Medium

DEF Dosing Valve - Data Erratic

Run Full DiagnosisView Related Faults

Scan Tool — in guided session

DVOM Testing — in guided session

Connector Pinout — in guided session

DieselVision™ Upload photos — DieselVision™ reads diagrams, connectors, and screens with precision.

Overview

Fault Code

SPN 4374 / FMI 19

Severity

Medium

Regen Inhibit

No

Inducement Risk

No

Component Location: DEF dosing valve is mounted on the DEF decomposition tube or mixing pipe, typically downstream of the DPF and upstream of the SCR catalyst on the exhaust aftertreatment assembly.

Common Symptoms

  • MIL lamp illuminated. DEF warning lamp on. Erratic or inconsistent DEF injection rates visible on scan tool. Fluctuating NOx readings downstream of SCR. Possible ammonia smell from exhaust due to inconsistent dosing. SCR efficiency codes may accompany. Engine may enter inducement strategy if fault persists. DEF consumption may be abnormally high or low compared to fuel usage.

Root Causes

  • [object Object]
  • [object Object]
  • [object Object]
  • [object Object]
  • [object Object]
  • [object Object]

Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.

AI walks you through every test — one step at a time. Plans start at $12.95/mo.

Start Guided DiagnosisSee How It Works

Derate Behavior

Mileage / Regen Notes

This fault typically does not directly inhibit DPF active regeneration, as the dosing valve is part of the SCR system (NOx reduction) rather than the DPF regen system. However, if the ACM detects unreliable dosing data, it may suspend DEF injection during regen events to prevent catalyst damage. Prolonged erratic dosing can lead to SCR efficiency faults which may eventually affect overall aftertreatment strategy. Monitor for companion DPF-related codes.

System Interactions

SPN 4374 FMI 19 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: No confirmed universal TSBs — verify in OEM service portal for specific make/model. Cummins has issued service letters regarding dosing valve connector corrosion on ISB/ISX platforms. Detroit Diesel has bulletins on DD13/DD15 DEF doser seal failures. Paccar has released updates for MX-13 dosing valve calibration. Always check for latest calibration updates for ACM before replacement.

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.

Deep-dive diagnostic page: SPN 4374 FMI 19 — 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.

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.EPA Aftertreatment & Emissions GuidelinesU.S. EPA heavy-duty diesel aftertreatment compliance, DPF/SCR regulations, and NOx standards.

Get weekly diesel diagnostic tips

Real-world fault code walkthroughs, wiring tips, and shop-tested fixes — free.

No spam. Unsubscribe anytime.

Get AI-Guided Diagnosis for SPN 4374 FMI 19

The diagnostic engine walks you through every physical test — step by step, on your phone, at the truck. No guessing. No wasted parts.

Run Full DiagnosisView Related Faults