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Fault Code Reference

SPN 4364 FMI 16AftertreatmentInducement Risk

SCR System - Data Valid But Above Normal

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Overview

Fault Code

SPN 4364 / FMI 16

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: SCR catalyst and DEF dosing injector are located in the aftertreatment assembly on the exhaust mid-pipe, typically mounted on or near the frame rail under the cab or behind the cab.

Common Symptoms

  • DEF quality warning lamp illuminated
  • Amber warning light active
  • SCR system efficiency reduced
  • Possible DEF consumption increase
  • NOx sensor readings elevated above threshold
  • Emissions system warning displayed

Root Causes

  • Insufficient DEF (diesel exhaust fluid) quality or contamination causing low NOx conversion efficiency
  • Faulty or degraded DEF dosing injector causing underdosing of urea
  • DEF supply module or pump malfunction reducing DEF flow rate
  • NOx sensor (outlet/downstream) drift or failure reporting falsely elevated NOx levels
  • SCR catalyst degraded or poisoned reducing conversion efficiency
  • DEF doser line restriction or crystallization blockage
  • DEF tank heater malfunction causing gel/freeze in cold conditions affecting DEF flow
  • ACM software or calibration issue misinterpreting NOx conversion ratio

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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

SPN 4364 FMI 16 indicates SCR NOx conversion efficiency is above the acceptable threshold (too much NOx passing through). This condition may inhibit or restrict active DPF regeneration to protect the aftertreatment system, and can trigger a derate or inducement strategy if SCR efficiency does not recover. Forced regeneration may be blocked until fault is resolved.

System Interactions

SPN 4364 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.

Deep-dive diagnostic page: SPN 4364 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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