SPN 677 FMI 2Electrical
Starter Motor - Data Erratic, Intermittent or Incorrect
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 677 / FMI 2
Category
Electrical
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Starter motor is mounted on the engine block near the flywheel housing, typically on the lower driver or passenger side of the engine.
Common Symptoms
- Starter motor cranks intermittently or erratically
- Engine fails to crank consistently when key is turned
- Starter engages but speed varies unpredictably
- Intermittent no-start condition
- Grinding or clicking noise during cranking attempts
Root Causes
- Faulty starter motor solenoid or internal contacts Loose or corroded battery cable connections Damaged wiring harness between ECM and starter relay Intermittent starter relay failure Poor ground connections at starter or engine block
Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.
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Derate Behavior
Power Derate
No
System Interactions
SPN 677 FMI 2 interacts with the following systems and may trigger cascading faults if not resolved promptly.
ECM communication — J1939 network faults can affect all connected modules
Engine protection — ECM may trigger derate to prevent damage
Aftertreatment — engine protection derates can affect regen strategy
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 677 FMI 2 — 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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