SPN 403 FMI 0EmissionsMedium
Exhaust Gas Recirculation Sensor A Circuit
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 403 / FMI 0
Category
Emissions
Severity
Medium
Regen Inhibit
No
Inducement Risk
No
Component Location: EGR valve and sensor assembly typically mounted on the intake manifold or exhaust crossover pipe near the engine's cylinder head.
Common Symptoms
- Illuminated MIL or Check Engine light
- Reduced engine power or derate condition
- Excessive black or white exhaust smoke
- Rough idle or unstable engine performance
- Failed emissions inspection or OBD readiness monitor not ready
- Increased fuel consumption
Root Causes
- EGR valve stuck open or failed mechanically
- EGR position sensor failure or drift out of range
- Excessive soot buildup on EGR valve and sensor
- Wiring harness damage, chafing, or connector corrosion at EGR sensor circuit
- EGR cooler failure causing sensor contamination
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Derate Behavior
Mileage / Regen Notes
SPN 403 FMI 0 can inhibit or abort active DPF regeneration due to inaccurate EGR flow data causing the ECM to restrict regen conditions to protect aftertreatment components.
System Interactions
SPN 403 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 403 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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