SPN 3509 FMI 5Lighting
Body Controller Lighting Output - Current Below Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 3509 / FMI 5
Category
Lighting
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Body control module is typically mounted in the cab behind the instrument panel or in an underdash electrical center.
Common Symptoms
- Exterior lights dim or inoperative
- Dash warning light for lighting system active
- Multiple lights on same circuit not functioning
- Intermittent light operation
- Body control module lighting fault code stored
Root Causes
- Open circuit in lighting harness Corroded or loose ground connection Failed body control module output driver Broken or damaged wiring to light assembly Poor connection at lighting connector
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Derate Behavior
Power Derate
No
System Interactions
SPN 3509 FMI 5 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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 3509 FMI 5 — 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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