SPN 204 FMI 0Fuel System
Injector Circuit Malfunction - Cylinder 3
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Overview
Fault Code
SPN 204 / FMI 0
Category
Fuel System
Derate Risk
Possible
Regen Inhibit
No
Inducement Risk
No
Component Location: Cylinder 3 fuel injector is located on the cylinder head at the third cylinder position in the engine firing order.
Common Symptoms
- Rough idle with visible shaking
- Misfire on cylinder 3
- Increased white or gray smoke from exhaust
- Loss of power under load
- Engine runs rough during cold start
- Check engine light illuminated
Root Causes
- Faulty fuel injector on cylinder 3 Damaged or corroded injector wiring harness Failed injector driver circuit in ECM Contaminated fuel causing injector sticking Loose or corroded injector connector
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Derate Behavior
Power Derate
Possible
System Interactions
SPN 204 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Fuel rail pressure — injector timing and quantity affected
Engine power output — derate may be triggered to protect injectors
Aftertreatment regen — low fuel pressure can prevent regen completion
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.
Replacing injectors without verifying fuel supply pressure — low supply pressure causes injector faults.
Ignoring fuel filter restriction — a clogged filter causes low rail pressure that mimics injector failure.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 204 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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