SPN 1485 FMI 2Turbo
Turbocharger Compressor Inlet Temperature - Data Erratic
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1485 / FMI 2
Category
Turbo
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: The turbocharger compressor inlet temperature sensor is located at the air intake system ahead of the turbocharger compressor inlet.
Common Symptoms
- Intermittent engine derate or loss of power
- Erratic boost pressure readings
- Poor engine performance during acceleration
- Check engine light illuminated
- Fluctuating intake air temperature readings on diagnostic software
- Excessive black or white smoke intermittently
Root Causes
- Faulty turbocharger inlet air temperature sensor Damaged or corroded wiring harness to the inlet air temperature sensor Intermittent connector issues at the sensor or ECM Water or contamination intrusion in sensor connector ECM software calibration issue
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Derate Behavior
Power Derate
No
System Interactions
SPN 1485 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.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1485 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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