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Fault Code Reference

SPN 2630 FMI 2AftertreatmentInducement Risk

Aftertreatment Intake NOx - Data Erratic

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Overview

Fault Code

SPN 2630 / FMI 2

Category

Aftertreatment

Derate Risk

No

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: Upstream (pre-SCR/pre-DPF) NOx sensor mounted in the exhaust pipe between the turbocharger outlet and the aftertreatment inlet, typically on the driver side of the vehicle.

Common Symptoms

  • Check engine light illuminated
  • Engine derate or power loss
  • NOx sensor implausibility fault logged
  • Increased DEF consumption
  • Aftertreatment system efficiency warnings
  • Poor emission system performance

Root Causes

  • Failed or degraded upstream NOx sensor (sensor poisoning from oil ash, sulfur, or coolant contamination) NOx sensor connector corrosion or moisture intrusion causing erratic signal Damaged or chafed NOx sensor wiring harness (intermittent open or short) NOx sensor heater circuit fault causing improper sensor warm-up and erratic readings ECU/ACM software anomaly or calibration mismatch requiring reflash Exhaust system air leak upstream of NOx sensor causing false low NOx readings Failed NOx sensor control module or integrated PCAN communication error High sulfur fuel use accelerating NOx sensor degradation Engine misfires or incomplete combustion causing NOx sensor signal instability ACM module internal fault or corrupted NOx sensor learned values

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Derate Behavior

Power Derate

No

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 2630 FMI 2 (Aftertreatment Intake NOx Data Erratic) will typically inhibit or suspend active DPF regeneration and SCR dosing optimization because the ACM cannot accurately determine engine-out NOx levels. Stationary and parked regeneration may be blocked. SCR urea dosing may default to a fixed or conservative strategy. Prolonged fault condition may result in derate and operator warning lamp illumination depending on OEM calibration thresholds.

System Interactions

SPN 2630 FMI 2 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 2630 FMI 2 — 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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