SPN 2629 FMI 0TurbochargerMedium
Turbo Compressor Inlet Temperature — High
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 2629 / FMI 0
Category
Turbocharger
Fault Type
sensor
FMI Category
performance
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: Turbo inlet — sensor mounted in air intake pipe at turbo compressor inlet
Common Symptoms
- Turbo inlet temperature warning active
- Possible power derate in hot conditions
- Air filter restriction may be contributing
Root Causes
- Clogged air filter restricting airflow and causing heat buildup
- High ambient temperature
- Turbo inlet temperature sensor failure
- Air intake system restriction
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Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
Air filter restriction common at any mileage. Sensor failures common 300k–500k miles.
System Interactions
SPN 2629 FMI 0 interacts with the following systems and may trigger cascading faults if not resolved promptly.
Boost pressure — engine air/fuel ratio and power output affected
EGR system — boost pressure affects EGR flow calculations
Aftertreatment — low boost can cause incomplete combustion and DPF loading
TSB Reference: Cummins TSB 4021550 — Turbo Inlet Temperature Diagnosis
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.
OEM Notes
Cummins
ISX15: Check air filter first — restriction causes heat buildup at turbo inlet.
Detroit
DD15: Check air intake system for leaks that could allow hot underhood air into intake.
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OEM System Resources
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 2629 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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