SPN 1221 FMI 10ABS
ABS Communication Error - Abnormal Rate of Change
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1221 / FMI 10
Category
ABS
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: ABS ECU is typically mounted on the frame rail near the rear axle or behind the cab.
Common Symptoms
- ABS warning lamp illuminated on dash
- ABS system disabled or unavailable
- Intermittent loss of ABS functionality
- Communication fault logged with ABS ECU
- Traction control system inactive
Root Causes
- Intermittent communication between ABS ECU and vehicle databus Faulty ABS ECU or internal processing issue CAN bus wiring harness damage or corrosion J1939 databus termination resistor failure Software version incompatibility between ABS and other modules
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Derate Behavior
Power Derate
No
System Interactions
SPN 1221 FMI 10 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1221 FMI 10 — 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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