SPN 3563 FMI 6Lighting
Left Turn Signal - Current Above Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 3563 / FMI 6
Category
Lighting
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Left turn signal lamps are mounted on the left front and rear corners of the vehicle with wiring routed through the chassis harness.
Common Symptoms
- Left turn signal inoperative or intermittent
- Warning lamp illuminated on dash for turn signal fault
- Turn signal bulbs not flashing on left side
- Dash indicator lamp flashing rapidly or not at all
Root Causes
- Short circuit in left turn signal wiring harness Faulty turn signal lamp socket with internal short Damaged or pinched wiring to left turn signal lamps Water intrusion in lamp housing causing short to ground Failed body control module or lighting control module
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Derate Behavior
Power Derate
No
System Interactions
SPN 3563 FMI 6 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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3563 FMI 6 — 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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