SPN 1277 FMI 0ABS/BrakesHigh
Brake Fluid Level Low
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1277 / FMI 0
Category
ABS/Brakes
Severity
High
Regen Inhibit
No
Inducement Risk
No
Component Location: Brake fluid reservoir is typically mounted on the firewall or frame rail near the brake master cylinder assembly.
Common Symptoms
- Low brake fluid warning light illuminated on dash
- ABS warning light active
- Reduced braking performance or soft brake pedal
- Brake pedal travel increased
- Driver notification message for brake system service
Root Causes
- Brake fluid leak at wheel cylinders or calipers Leaking brake master cylinder Worn brake pads causing fluid level drop Faulty brake fluid level sensor Brake line or hose leak
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System Interactions
SPN 1277 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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Deep-dive diagnostic page: SPN 1277 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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