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Fault Code Reference

SPN 3610 FMI 0AftertreatmentInducement Risk

NOx Sensor 2 - Data Valid But Above Normal

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Overview

Fault Code

SPN 3610 / FMI 0

Category

Aftertreatment

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: NOx sensor 2 is located on the exhaust outlet of the SCR catalyst, typically mounted on the tailpipe or SCR outlet cone on the right or underside of the vehicle frame.

Common Symptoms

  • Check engine light illuminated
  • Engine derate or power loss
  • NOx sensor out of range fault active
  • Elevated NOx readings displayed
  • SCR system efficiency warning

Root Causes

  • Failed or degraded downstream NOx sensor (sensor 2) reporting erroneously high NOx values SCR catalyst degradation or poisoning reducing NOx conversion efficiency DEF dosing system malfunction causing insufficient urea injection (clogged injector, failed DEF pump) DEF quality issue - diluted, contaminated, or incorrect concentration of urea solution DEF doser or injector not opening properly due to deposits or electrical fault Exhaust system leak upstream of SCR allowing unfiltered exhaust bypass NOx sensor 2 connector corrosion or poor electrical connection causing false high readings Upstream NOx sensor (sensor 1) fault leading to incorrect dosing strategy ACM software or calibration issue resulting in improper DEF dosing commands DPF excessive soot load causing elevated exhaust temperatures affecting SCR performance

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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.

System Interactions

SPN 3610 FMI 0 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 3610 FMI 0 — 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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