SPN 1637 FMI 31Body
Traction Control 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 1637 / FMI 31
Category
Body
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The traction control switch is typically mounted on the dashboard or center console within easy reach of the driver.
Common Symptoms
- Traction control warning light illuminated on dash
- Traction control system inoperative or disabled
- ABS warning light may also illuminate
- Vehicle stability control may be disabled
- Diagnostic trouble code stored in BCM
Root Causes
- Faulty traction control switch Damaged wiring harness to traction control switch Intermittent switch contact or corrosion ECU configuration mismatch for traction control system Poor ground connection at switch circuit
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Derate Behavior
Power Derate
No
System Interactions
SPN 1637 FMI 31 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
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1637 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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