SPN 124 FMI 0ABS/BrakesHigh
Wheel Speed Sensor Circuit Range/Performance (Right Rear)
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 124 / FMI 0
Category
ABS/Brakes
Severity
High
Regen Inhibit
No
Inducement Risk
No
Component Location: The right rear wheel speed sensor is mounted on the axle housing near the right rear wheel assembly.
Common Symptoms
- ABS warning light illuminated on dash
- ABS system disabled or non-functional
- Traction control system disabled
- Stability control warning light active
- No derate or engine impact observed
Root Causes
- Faulty wheel speed sensor Damaged or contaminated tone ring Excessive air gap between sensor and tone ring Damaged wiring harness or connectors Corroded or loose sensor mounting
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System Interactions
SPN 124 FMI 0 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 124 FMI 0 — 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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