SPN 108 FMI 2Engine
Barometric Pressure - Data Erratic, Intermittent or Incorrect
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 108 / FMI 2
Category
Engine
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The barometric pressure sensor is typically integrated into the ECM or mounted on the intake manifold area depending on engine model.
Common Symptoms
- Poor engine performance at altitude
- Black smoke during acceleration
- Low power complaints
- Hard starting in certain conditions
- Excessive fueling or lean conditions
- Failed emissions testing
- Intermittent check engine light
Root Causes
- Faulty barometric pressure sensor Wiring harness damage or corrosion in sensor circuit Intermittent connector issues at barometric pressure sensor ECM internal fault affecting sensor signal processing Environmental contamination of sensor element
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Derate Behavior
Power Derate
No
System Interactions
SPN 108 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.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 108 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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