AI Diesel Tech

Fault Code Reference

SPN 3359 FMI 31AftertreatmentInducement Risk

NOx Emission Operator Inducement - Condition Exists

Run Full DiagnosisView Related FaultsSee OEM System Guide

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 3359 / FMI 31

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: NOx sensors are located in the exhaust system upstream and downstream of the SCR catalyst, with DEF dosing system on the chassis frame.

Common Symptoms

  • Warning lamp illuminated on dash
  • Operator inducement active message displayed
  • Reduced vehicle performance or speed limitation
  • Driver notification of emissions system fault
  • NOx levels exceeding regulatory thresholds

Root Causes

  • SCR system efficiency below threshold triggering operator inducement (OBD/EPA compliance fault)
  • DEF (Diesel Exhaust Fluid) quality out of specification or diluted with water
  • DEF doser/injector clogged or failed causing insufficient urea injection
  • Upstream or downstream NOx sensor failed or reading incorrectly, causing false NOx efficiency calculation
  • SCR catalyst degraded, poisoned, or thermally damaged reducing NOx conversion efficiency
  • DEF tank level sensor fault or DEF tank empty causing dosing interruption
  • DEF supply pump failure resulting in low or no DEF delivery pressure
  • Unanswered or uncleared previous NOx-related active faults leading to escalated inducement
  • ACM software issue or calibration mismatch causing incorrect NOx efficiency evaluation
  • Tampering or defeat device detected by OBD monitoring system

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

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

Active operator inducement condition (SPN 3359 FMI 31) typically inhibits or severely restricts active DPF regeneration and may derate engine power progressively. SCR dosing may be suspended, preventing NOx reduction. If inducement escalates, forced idle or engine shutdown may occur per EPA regulations.

System Interactions

SPN 3359 FMI 31 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 3359 FMI 31 — 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.

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 3359 FMI 31

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 FaultsSee OEM System Guide