SPN 597 FMI 31Electrical
Cruise Control Enable Switch - Condition Exists
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 597 / FMI 31
Category
Electrical
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Cruise control enable switch is typically located on the dash-mounted steering column stalk or a separate switch panel on the dashboard.
Common Symptoms
- Cruise control inoperative or will not engage
- Cruise control warning lamp illuminated on dash
- Intermittent cruise control operation
- Cruise control disengages unexpectedly
Root Causes
- Faulty cruise control enable switch Damaged or corroded wiring harness to cruise control switch Poor electrical connection at switch connector Water intrusion or corrosion in switch assembly Brake pedal switch interference with cruise enable signal
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Derate Behavior
Power Derate
No
System Interactions
SPN 597 FMI 31 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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 597 FMI 31 — 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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