SPN 405 FMI 0EGR
EGR Sensor A Circuit Low
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 405 / 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 EGR mixer on the engine, with two pressure hose ports sampling differential pressure across the EGR system.
Common Symptoms
- EGR valve position feedback reads abnormally low or zero on diagnostic scan tool
- Engine derate or reduced power mode active
- Excessive black or gray exhaust smoke under load
- Hard start or rough idle due to improper EGR flow control
- MIL or Check Engine light illuminated with active fault logged
- Failed emissions test due to uncontrolled EGR operation
Root Causes
- Faulty EGR differential pressure sensor Damaged wiring harness or connector to EGR differential pressure sensor Corroded or damaged sensor connector pins Short to ground in sensor signal circuit Failed ECM internal circuit
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Derate Behavior
Power Derate
No
System Interactions
SPN 405 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 405 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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