SPN 1323 FMI 18Turbocharger
Turbocharger #1 Compressor Intake Pressure - Data Valid But Below Normal
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Overview
Fault Code
SPN 1323 / FMI 18
Category
Turbocharger
Derate Risk
Yes
Regen Inhibit
No
Inducement Risk
No
Component Location: The turbocharger compressor intake pressure sensor is typically mounted on the inlet side of the turbocharger or in the fresh air intake ductwork.
Common Symptoms
- Reduced engine power and acceleration
- Lack of turbocharger boost pressure
- Black or gray smoke under load
- Engine derate or limp mode activation
- Poor throttle response
Root Causes
- Boost pressure leak in intake system upstream of sensor Clogged or restricted air filter Faulty turbocharger compressor intake pressure sensor Damaged or collapsed intake ductwork Turbocharger compressor wheel damage or failure
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Derate Behavior
Power Derate
Yes
System Interactions
SPN 1323 FMI 18 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
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 1323 FMI 18 — 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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