SPN 1110 FMI 18Engine Protection
Coolant Filter Differential Pressure - Data Valid But Below Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 1110 / FMI 18
Category
Engine Protection
Derate Risk
No
Regen Inhibit
No
Inducement Risk
No
Component Location: Coolant filter assembly is typically mounted on the side of the engine block or near the water pump housing.
Common Symptoms
- Check engine light illuminated
- SPN 1110 FMI 18 logged in fault memory
- Low differential pressure reading across coolant filter
- Filter restriction reading below expected range
- No drivability concerns
Root Causes
- Coolant filter bypass valve stuck open, reducing differential pressure across filter Coolant filter element missing, collapsed, or improperly installed Coolant filter housing bypass spring weak or failed Low coolant flow rate due to coolant pump wear or cavitation Sensor or differential pressure switch failed low/open circuit Air entrainment in cooling system reducing effective flow restriction Incorrect coolant filter installed (wrong restriction rating for application)
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Derate Behavior
Power Derate
No
System Interactions
SPN 1110 FMI 18 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
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 1110 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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