SPN 400 FMI 0EGR
EGR Flow Malfunction
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Overview
Fault Code
SPN 400 / FMI 0
Category
EGR
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR valve and flow sensor are typically mounted on the intake manifold or EGR cooler assembly near the engine block.
Common Symptoms
- Check engine light / MIL illuminated
- Excessive black smoke during acceleration
- Reduced engine power and performance
- Poor fuel economy
- Rough idle or surging
- Failed emissions test
- EGR valve stuck open condition
Root Causes
- EGR valve stuck open or failed in open position causing excessive flow Clogged or restricted EGR cooler reducing flow measurement accuracy Faulty differential pressure sensor (delta-P) providing incorrect flow data Carbon buildup in EGR passages or intake manifold restricting flow EGR cooler bypass valve failure affecting thermal management and flow Intake throttle valve stuck or sluggish affecting EGR flow ratio Air leaks in EGR piping or gaskets causing unmeasured flow loss MAF or MAP sensor out of calibration causing flow calculation errors ECM software or calibration issue misinterpreting flow signal
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Derate Behavior
Power Derate
No
Mileage / Regen Notes
SPN 400 FMI 0 (data valid but above normal range) may inhibit or interrupt active DPF regeneration due to excessive EGR flow skewing combustion and exhaust temperature control; regen lockout is common until fault is resolved.
System Interactions
SPN 400 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
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
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 400 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.
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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