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Fault Code Reference

SPN 2631 FMI 1EGRHighInducement Risk

EGR Mass Flow Rate - Low

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Overview

Fault Code

SPN 2631 / FMI 1

Category

EGR

Severity

High

Derate Risk

Yes

Regen Inhibit

No

Inducement Risk

Yes — SCR inducement possible

Component Location: EGR valve and mass flow sensor are typically mounted on the intake manifold or EGR cooler assembly near the engine block.

Common Symptoms

  • Engine derate with reduced power and speed limiting. Rough idle or surging at idle. Check engine light illuminated. Higher than normal exhaust temperatures. Increased NOx emissions (may trigger related SCR faults). Black smoke under load. Poor fuel economy. Engine may run hotter than normal due to lack of EGR cooling effect. Possible limp mode activation on highway.

Root Causes

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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

This fault typically does NOT directly inhibit active DPF regeneration. However, low EGR flow causes elevated combustion temperatures and increased NOx output, which increases soot loading in the DPF and may lead to more frequent regen requests. If derate is severe enough to limit engine load, regen temperatures may be harder to achieve and regens may take longer or fail to complete. Monitor DPF soot load — if this code runs extended, expect accelerated soot accumulation. Address EGR issue before performing forced regen to avoid repeat failures.

System Interactions

SPN 2631 FMI 1 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. Cummins ISX/ISB: Check for bulletins related to EGR valve carbon buildup and updated cleaning procedures. Detroit DD13/DD15: Check for EGR cooler warranty extensions and updated cooler designs. Paccar MX: Check for EGR valve calibration updates. Always search by engine serial number for applicable campaigns or extended coverage.

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 2631 FMI 1 — 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.

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