SPN 1251 FMI 5ABS
ABS Modulator Valve - Rear Left - Current Below Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1251 / FMI 5
Category
ABS
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The rear left ABS modulator valve is integrated into the ABS valve block mounted on the rear axle frame rail or suspension assembly.
Common Symptoms
- ABS warning lamp illuminated on dash
- Reduced or no ABS functionality on rear left wheel
- Wheel lockup during braking on rear left position
- Traction control system disabled or inoperative
- Stability control warnings or malfunction indicators
Root Causes
- Open circuit in wiring harness to rear left ABS modulator valve Damaged or corroded connector at rear left ABS modulator valve Failed rear left ABS modulator solenoid valve Chafed or broken wires in chassis harness near rear axle Faulty ABS ECU output driver circuit
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Derate Behavior
Power Derate
No
System Interactions
SPN 1251 FMI 5 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 1251 FMI 5 — 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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