AI Diesel Tech

Fault Code Reference

SPN 302 FMI 0Ignition/MisfireHigh

Cylinder 2 Misfire Detected

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Overview

Fault Code

SPN 302 / FMI 0

Category

Ignition/Misfire

Severity

High

Regen Inhibit

No

Inducement Risk

No

Component Location: Cylinder 2 is the second cylinder in the engine firing order, located on the engine block; exact position varies by engine configuration (inline or V-type).

Common Symptoms

  • Rough idle or engine roughness at low RPM
  • Loss of power or reduced engine performance
  • Increased fuel consumption
  • Visible black or white exhaust smoke
  • Engine vibration felt in cab
  • Check Engine Light or MIL illuminated

Root Causes

  • Faulty or failed fuel injector on cylinder 2
  • Low compression in cylinder 2 due to worn rings, valves, or head gasket failure
  • Damaged or fouled glow plug on cylinder 2 (if applicable)
  • Camshaft or rocker arm wear causing improper valve timing on cylinder 2
  • Air or fuel delivery issue specific to cylinder 2 (e.g., cracked fuel line, restricted passage)

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Derate Behavior

Mileage / Regen Notes

Active or parked DPF regeneration will be inhibited or blocked when a cylinder misfire is detected, as unburned fuel entering the aftertreatment system poses a risk of DPF damage or uncontrolled regeneration event.

System Interactions

SPN 302 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.

Deep-dive diagnostic page: SPN 302 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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