SPN 406 FMI 0EGR
EGR Sensor A Circuit High
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 406 / FMI 0
Category
EGR
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR differential pressure sensor is typically mounted on or near the EGR cooler or intake manifold.
Common Symptoms
- EGR valve position reads at or near maximum scale on scan tool
- Hard start or no-start condition due to fueling compensation errors
- Black or excessive smoke from exhaust under load
- Engine derate or reduced power event active
- MIL or Check Engine lamp illuminated with active fault logged
- Rough idle or unstable idle from incorrect EGR feedback
Root Causes
- EGR differential pressure sensor supply voltage shorted to high voltage source Damaged or chafed wiring harness causing short to voltage on signal wire Faulty EGR differential pressure sensor with internal failure driving signal high Corroded or contaminated sensor connector causing elevated resistance or voltage offset Failed or out-of-range EGR pressure sensor due to soot or oil contamination on ports ECM sensor reference voltage circuit fault causing elevated signal reading
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Derate Behavior
Power Derate
No
System Interactions
SPN 406 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 406 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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