SPN 306 FMI 0Ignition/MisfireHigh
Cylinder 6 Misfire Detected
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Overview
Fault Code
SPN 306 / FMI 0
Category
Ignition/Misfire
Severity
High
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 6 is typically the rearmost cylinder on inline-6 engines or the rear cylinder on the passenger side of V-configuration diesel engines.
Common Symptoms
- Rough idle or engine vibration at low RPM
- Loss of power or sluggish acceleration
- Excessive black or white smoke from exhaust
- Check Engine Light or MIL illuminated
- Increased fuel consumption
- Engine knock or misfiring sound from cylinder 6 bank
Root Causes
- Failed or fouled fuel injector on cylinder 6
- Low compression in cylinder 6 due to worn rings or damaged valve
- Faulty glow plug on cylinder 6 causing poor combustion
- Contaminated or aerated fuel supply to cylinder 6
- Cracked or leaking cylinder 6 combustion seal or head gasket
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Derate Behavior
Mileage / Regen Notes
Active cylinder 6 misfire will inhibit DPF regeneration due to raw fuel and combustion byproduct loading risk; high soot load events may occur and passive regen efficiency will be severely reduced.
System Interactions
SPN 306 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 306 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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