SPN 1086 FMI 4ABS
Brake Application Pressure - Voltage 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 1086 / FMI 4
Category
ABS
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Brake application pressure sensor is typically mounted on the brake valve or air system manifold near the driver-side frame rail.
Common Symptoms
- ABS warning lamp illuminated on dash
- Traction control malfunction or disabled
- Stability control system inactive
- Brake pressure gauge reading low or zero
- Fault code SPN 1086 FMI 4 active
- ABS system may default to non-ABS braking
Root Causes
- Faulty brake application pressure sensor Damaged or corroded wiring harness to pressure sensor Low sensor supply voltage from ABS module Shorted sensor signal circuit to ground Defective ABS control module
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Derate Behavior
Power Derate
No
System Interactions
SPN 1086 FMI 4 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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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1086 FMI 4 — 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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