SPN 1633 FMI 2ABS
Electronic Stability Control - Data Erratic/Intermittent
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1633 / FMI 2
Category
ABS
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The ABS/ESC controller is typically mounted on the frame rail or chassis near the brake system components, with wheel speed sensors at each wheel hub.
Common Symptoms
- ABS warning lamp illuminated on dash
- Electronic Stability Control (ESC) system disabled or inactive
- Intermittent ABS activation during normal driving
- Traction control malfunction light on
- Vehicle stability control intervention erratic or unpredictable
Root Causes
- Faulty wheel speed sensor providing erratic signal Damaged or corroded wiring harness to wheel speed sensors Faulty ABS module or internal ESC processor Intermittent connector corrosion at ABS controller Damaged tone ring or excessive wheel bearing play
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Derate Behavior
Power Derate
No
System Interactions
SPN 1633 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 1633 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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