SPN 111 FMI 1CoolingHighRegen Inhibit
Engine Coolant Level — Low
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
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Overview
Fault Code
SPN 111 / FMI 1
Category
Cooling
Fault Type
sensor
FMI Category
performance
Severity
High
Derate Risk
Yes
Regen Inhibit
Yes — active regen blocked
Inducement Risk
No
Component Location: Coolant level sensor — on overflow tank or radiator
Common Symptoms
- Coolant level low
- Coolant level warning lamp on
- Engine overheating risk
- Coolant loss
Root Causes
- Coolant leak — external
- EGR cooler internal leak
- Head gasket failure
- Coolant not filled to correct level
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Derate Behavior
Power Derate
Yes
Active Regen Inhibited
This fault prevents the DPF from completing an active regeneration cycle. DPF soot load will increase until the fault is resolved.
Mileage / Regen Notes
Coolant leaks can occur at any mileage. EGR cooler failure common at 300k–500k miles.
System Interactions
SPN 111 FMI 1 interacts with the following systems and may trigger cascading faults if not resolved promptly.
TSB Reference: Cummins TSB 4021410 — Coolant Level Low 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
X15: Check EGR cooler for internal leak.
Detroit
DD15: Check coolant filter housing for leaks.
Volvo
MP8: Check deaeration tank for air pockets.
Related Faults in This Category
OEM System Resources
ASE Training Resources
Diagnostic Engine v7.0
Related Diagnostic Articles
Deep-dive diagnostic page: SPN 111 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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