SPN 411 FMI 31EGR SystemHigh
EGR Differential Pressure - Condition Exists (EGR Flow Monitoring Fault)
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Overview
Fault Code
SPN 411 / FMI 31
Category
EGR System
Fault Type
sensor
FMI Category
condition exists
Severity
High
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR differential pressure sensor mounted on the engine or firewall with two hoses connecting to EGR valve inlet and outlet pressure taps. EGR valve on exhaust manifold or EGR cooler outlet - typically driver side of engine.
Common Symptoms
- EGR differential pressure fault active - EGR flow monitoring condition exists
- Engine derate active - ECM cannot confirm EGR flow is within specification
- Possible black smoke under load - EGR flow uncontrolled
- EGR system fault lamp illuminated
- Possible companion faults: SPN 2659/2 (EGR mass flow erratic), SPN 544/4 (EGR valve position low)
- EGR differential pressure reading outside expected range for current operating conditions
Root Causes
- EGR differential pressure sensor failure - sensor reading outside expected range
- EGR differential pressure sensor hoses blocked or disconnected
- EGR valve stuck open or closed - differential pressure not matching commanded EGR flow
- EGR cooler restriction - cooler partially blocked reducing EGR flow
- EGR differential pressure sensor connector - corroded or loose connection
- EGR system leak - air or exhaust leak affecting differential pressure reading
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Derate Behavior
Power Derate
Yes
Mileage / Regen Notes
EGR valve carbon buildup increases with mileage. EGR cooler restriction increases with mileage and high-idle operation.
System Interactions
SPN 411 FMI 31 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021889 - EGR Differential Pressure Sensor Diagnosis; Detroit TSB 17-015 - EGR System Differential Pressure Fault
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.
OEM Notes
Cummins
X15: EGR differential pressure sensor hose blockage with soot is common. Inspect and clean hoses before replacing sensor. INSITE EGR system test required.
Detroit
DD15: EGR valve carbon buildup causing incorrect differential pressure is common on high-mileage DD15. DDDL EGR valve test required.
PACCAR
MX-13: EGR cooler restriction is a common cause of low differential pressure on MX-13. Inspect EGR cooler before condemning sensor or valve.
Volvo
MP8: EGR differential pressure sensor connector corrosion is common on MP8. Clean connector before replacing sensor. PTT EGR test required.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 411 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.
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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