SPN 2623 FMI 2Chassis
Vehicle Distance - 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 2623 / FMI 2
Category
Chassis
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Wheel speed sensors are mounted at each wheel hub assembly, typically near the brake rotor or axle tone ring.
Common Symptoms
- Speedometer fluctuation or erratic reading
- Cruise control disengagement or inoperative
- Inaccurate distance or mileage recording
- ABS or traction control system faults
- Intermittent loss of vehicle speed display
- Transmission shift issues or unexpected gear changes
Root Causes
- Faulty wheel speed sensor Damaged or corroded wiring harness to speed sensor Faulty ABS module or ECU communication issue Tone ring damage or missing teeth Poor sensor air gap or mounting
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Derate Behavior
Power Derate
No
System Interactions
SPN 2623 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 2623 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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