SPN 1247 FMI 4ABS
Wheel Speed Sensor - Rear Left Inner - Voltage Below Normal
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1247 / FMI 4
Category
ABS
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The rear left inner wheel speed sensor is mounted on the rear axle assembly near the brake rotor or hub with the tone ring.
Common Symptoms
- ABS warning lamp illuminated on dash
- Traction control disabled or warning light active
- Stability control system inoperative
- Erratic speedometer reading or no speedometer function
- ABS system may default to non-ABS braking mode
Root Causes
- Damaged or corroded wheel speed sensor wiring harness Faulty rear left inner wheel speed sensor Poor electrical connection at sensor connector Excessive air gap between sensor and tone ring Damaged tone ring on wheel hub
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Derate Behavior
Power Derate
No
System Interactions
SPN 1247 FMI 4 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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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1247 FMI 4 — 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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