SPN 430 FMI 0EmissionsMedium
Catalyst System Efficiency Below Threshold (Bank 2)
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Overview
Fault Code
SPN 430 / FMI 0
Category
Emissions
Severity
Medium
Regen Inhibit
No
Inducement Risk
No
Component Location: SCR catalyst is located in the aftertreatment system on the exhaust outlet side of the vehicle, typically mounted under the frame rails or vertically on the chassis behind the cab.
Common Symptoms
- Check engine light illuminated (MIL on)
- DEF/SCR system warning lamp active
- Reduced engine power or derate condition
- Excessive NOx readings at tailpipe
- Failed emissions inspection or OBD readiness monitor
- Repeated or continuous active regen cycles
Root Causes
- SCR catalyst degradation or poisoning (sulfur, oil ash, coolant contamination)
- DEF quality issue or urea crystal buildup in dosing system
- DEF doser/injector malfunction causing incorrect urea delivery
- NOx sensor (upstream or downstream Bank 2) failure giving false efficiency reading
- Exhaust leaks upstream of SCR catalyst skewing NOx conversion calculation
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Derate Behavior
Mileage / Regen Notes
SPN 430 FMI 0 can inhibit or interrupt active DPF regen if SCR efficiency is critically low; repeated failed regens may elevate soot load and worsen catalyst condition over time.
System Interactions
SPN 430 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 430 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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