SPN 4752 FMI 1Engine Protection
Engine Crankcase Pressure - Data Valid But Below Normal
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DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 4752 / FMI 1
Category
Engine Protection
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Crankcase pressure sensor is typically mounted on the valve cover or crankcase vent housing on the top or side of the engine block, near the CCV filter assembly.
Common Symptoms
- Check engine light or malfunction indicator lamp illuminated
- Engine protection derate may occur
- Crankcase pressure sensor reading abnormally low
- No noticeable performance issues in most cases
- Fault code logged in ECM memory
Root Causes
- Clogged or restricted crankcase ventilation (CCV) filter element
- Collapsed or kinked CCV hose or tubing
- Failed or stuck-open crankcase pressure regulator valve
- Crankcase pressure sensor fault or drift below calibration
- Air leak in CCV system plumbing causing false low reading
- Restricted oil drain from CCV separator back to crankcase
- Sensor supply voltage or ground issue causing low signal
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Derate Behavior
Power Derate
No
System Interactions
SPN 4752 FMI 1 interacts with the following systems and may trigger cascading faults if not resolved promptly.
ECM communication — J1939 network faults can affect all connected modules
Engine protection — ECM may trigger derate to prevent damage
Aftertreatment — engine protection derates can affect regen strategy
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
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Related Diagnostic Articles
Deep-dive diagnostic page: SPN 4752 FMI 1 — 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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