SPN 627 FMI 3Fuel SystemMedium
Injector Power Supply - Voltage High
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Overview
Fault Code
SPN 627 / FMI 3
Category
Fuel System
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: Injector power supply originates at the ECM, routed through the engine valve cover harness to individual fuel injectors mounted on the cylinder head.
Common Symptoms
- Check engine light illuminated. Hard starting or no start condition. Rough idle or engine misfires. One or more injectors not firing. Engine running rough under load. Possible white or black smoke at startup. Reduced power complaints. Injector buzz test may show weak or no response from one or more cylinders.
Root Causes
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
This fault typically does not directly inhibit active DPF regeneration. However, if the high voltage condition causes injector malfunction or misfires, the ECM may detect poor combustion quality and postpone or abort active regen to prevent unburned fuel from damaging the aftertreatment system. If accompanied by multiple cylinder faults, expect regen lockout until injector operation is restored.
System Interactions
SPN 627 FMI 3 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
TSB Reference: No confirmed universal TSBs — verify in OEM service portal. Cummins ISX/ISB: Check for bulletins related to injector harness chafing at rocker cover pass-through. Detroit DD13/DD15: Review bulletins for valve cover harness connector issues. Paccar MX: Check for injector harness routing bulletins near turbo heat shield.
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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 627 FMI 3 — 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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