SPN 2631 FMI 3EGRMedium
EGR Mass Flow Rate Sensor - Voltage High
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 2631 / FMI 3
Category
EGR
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: The EGR mass flow sensor is typically mounted in the EGR cooler outlet or intake manifold to measure recirculated exhaust gas flow.
Common Symptoms
- Check engine light illuminated. MIL lamp on. Reduced engine power or torque in some conditions. Poor throttle response during acceleration. EGR system may default to closed position. Possible elevated NOx emissions. Rough idle in some applications. Black smoke under load if EGR defaults open. Scan tool shows EGR mass flow sensor voltage pegged high (near 5V or above).
Root Causes
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
This fault typically does NOT inhibit active DPF regeneration directly. However, if the ECM cannot accurately calculate EGR flow, it may affect overall emissions calculations and engine-out soot estimates. In some calibrations, multiple EGR-related faults together may delay or inhibit regen until the primary fault is resolved. Monitor regen status with scan tool if DPF soot load is climbing.
System Interactions
SPN 2631 FMI 3 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 and ISB platforms have known issues with EGR sensor harness chafing near cooler mounting brackets. Detroit DD13/DD15 have reported connector heat damage issues. Check OEM portal for platform-specific service letters.
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 2631 FMI 3 — 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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