SPN 2271 FMI 0O2Sensor
O2 Sensor Signal Stuck Rich Bank 1 Sensor 2
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 2271 / FMI 0
Category
O2Sensor
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The downstream oxygen sensor (Bank 1 Sensor 2) is mounted in the exhaust system after the diesel oxidation catalyst or DPF.
Common Symptoms
- Check engine light illuminated
- Poor fuel economy
- Black smoke from exhaust under load
- Engine derate or reduced power
- Elevated exhaust temperatures
- DPF regeneration occurs more frequently
Root Causes
- Faulty downstream oxygen sensor Exhaust leak upstream of the sensor Carbon buildup or soot contamination on sensor element Fuel system issue causing rich combustion Damaged or corroded sensor wiring harness
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Derate Behavior
Power Derate
No
System Interactions
SPN 2271 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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OEM System Resources
ASE Training Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 2271 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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