What are the symptoms of SPN 111 FMI 18?

Low coolant warning light illuminated on dash. MIL or check engine light active. Possible engine overheating or elevated coolant temperature. White steam or coolant smell from engine compartment. Coolant pooling under vehicle after parking. Sweet smell from HVAC vents (indicates heater core leak). Engine may go into protective derate mode. In severe cases, engine may shut down to prevent damage. Coolant reservoir visibly low or empty. Bubbling in coolant overflow tank (possible head gasket issue).

What causes SPN 111 FMI 18?

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How do I diagnose SPN 111 FMI 18?

Full step-by-step DVOM tests, electrical procedures, and connector pinout data for SPN 111 FMI 18 are available inside the AI Diesel Tech guided diagnostic session. The AI walks you through every test — one step at a time.

SPN 111 FMI 18EngineHigh

Engine Coolant Level - Low

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Overview

Fault Code

SPN 111 / FMI 18

Common Symptoms

Low coolant warning light illuminated on dash. MIL or check engine light active. Possible engine overheating or elevated coolant temperature. White steam or coolant smell from engine compartment. Coolant pooling under vehicle after parking. Sweet smell from HVAC vents (indicates heater core leak). Engine may go into protective derate mode. In severe cases, engine may shut down to prevent damage. Coolant reservoir visibly low or empty. Bubbling in coolant overflow tank (possible head gasket issue).

Root Causes

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Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.

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Derate Behavior

Power Derate

Yes

Mileage / Regen Notes

Low coolant level typically does not directly inhibit active DPF regeneration. However, if coolant loss leads to elevated coolant temperature (SPN 110 faults), the ECM will inhibit active regen to prevent additional heat load on an already overheating engine. Critical note: Internal coolant leak into combustion chamber (head gasket) or EGR cooler failure can contaminate DPF with coolant residue, causing increased soot loading and potential DPF damage. If coolant consumption is present with no external leaks, inspect DPF for white calcium/silicate deposits which indicate coolant contamination.

System Interactions

SPN 111 FMI 18 interacts with the following systems and may trigger cascading faults if not resolved promptly.

TSB Reference: No confirmed universal TSBs — verify in OEM service portal. Cummins ISX engines have known EGR cooler failure bulletins that cause coolant loss. Detroit DD13/DD15 have documented EGR cooler and water pump TSBs. PACCAR MX-13 has water pump weep hole and thermostat housing leak service letters. Always check OEM portal for current bulletins specific to engine serial number.

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

SPN 5246-31SCR NOx Efficiency Low SPN 4364-18DEF Dosing Below Normal SPN 3251-0DPF Differential Pressure High SPN 157-18Fuel Rail Pressure Low

OEM System Resources

Cummins Fault Codes Detroit Diesel Fault Codes PACCAR Fault Codes Volvo Fault Codes Freightliner Fault Codes Mack Fault Codes

ASE Training Resources

Why ASE Certification Matters How ASE Tests Work ASE Study Tips ASE vs AI Diesel Tech Certification Paths Get Started with ASE

Diagnostic Engine v7.0

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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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