SPN 1247 FMI 2ABS
Wheel Speed Sensor - Rear Left Inner - Data Erratic/Intermittent
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1247 / FMI 2
Category
ABS
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The rear left inner wheel speed sensor is mounted on the axle assembly near the rear left inner wheel hub.
Common Symptoms
- ABS warning lamp illuminated on dash
- Traction control light active
- ABS system deactivated or reduced function
- Intermittent wheel speed signal loss
- Anti-lock brake system malfunction
- Stability control disabled warning
Root Causes
- Damaged or contaminated wheel speed sensor tone ring Faulty wheel speed sensor or internal sensor failure Damaged wiring harness or corroded connector at the sensor Excessive wheel bearing play or air gap issue between sensor and tone ring Water or debris intrusion into the sensor connector
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Derate Behavior
Power Derate
No
System Interactions
SPN 1247 FMI 2 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 1247 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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