SPN 402 FMI 0EGR
EGR Flow Excessive Detected
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Overview
Fault Code
SPN 402 / FMI 0
Category
EGR
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR valve is mounted on the intake manifold with the EGR cooler positioned in the exhaust gas recirculation circuit.
Common Symptoms
- Black smoke from exhaust
- Rough idle or surging
- Reduced engine power
- Increased fuel consumption
- Check engine light illuminated
- Failed emissions test
- Turbo boost lower than normal
Root Causes
- EGR valve stuck open or not fully closing, allowing excessive exhaust gas recirculation flow beyond commanded limits EGR cooler bypass valve failed in open position, reducing restriction and increasing flow rate Intake throttle valve (ITV) stuck open or failed, reducing backpressure differential needed to regulate EGR flow Faulty EGR differential pressure sensor providing falsely high flow readings to the ECM Excessive carbon buildup on EGR valve seat preventing proper sealing and causing uncontrolled flow
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Derate Behavior
Power Derate
No
Mileage / Regen Notes
Excessive EGR flow (FMI 0) can inhibit or abort active DPF regeneration by reducing exhaust temperatures below the threshold needed for DPF oxidation; the ECM may delay or block regen requests until EGR flow is within acceptable range.
System Interactions
SPN 402 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 402 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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