SPN 301 FMI 0Ignition/MisfireHigh
Cylinder 1 Misfire Detected
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 301 / FMI 0
Category
Ignition/Misfire
Severity
High
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 1 is typically the frontmost cylinder on the driver side of the engine block, nearest the front accessory drive.
Common Symptoms
- Rough idle or engine roughness at low RPM
- Loss of power or reduced acceleration
- Excessive exhaust smoke (black or white)
- Check engine light or MIL illuminated
- Increased fuel consumption
- Engine vibration felt through cab or chassis
Root Causes
- Faulty or worn fuel injector on cylinder 1 (sticking, leaking, or failed)
- Low compression in cylinder 1 (worn rings, damaged valves, or blown head gasket)
- Failed or degraded glow plug on cylinder 1 (cold-start misfire)
- Air in fuel system causing intermittent fuel delivery disruption
- Rocker arm, pushrod, or valve train damage affecting cylinder 1 timing
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Derate Behavior
Mileage / Regen Notes
Active and parked DPF regeneration will be inhibited or interrupted when a cylinder misfire is detected, as raw fuel and unburned hydrocarbons entering the aftertreatment system risk DPF damage or uncontrolled exotherm.
System Interactions
SPN 301 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 301 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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