SPN 111 FMI 4Engine ProtectionMedium
Engine Coolant Level Sensor — Voltage Below Normal
Scan Tool — in guided session
DVOM Testing — in guided session
Connector Pinout — in guided session
DieselVision™ Upload photos — DieselVision™ reads diagrams, connectors, and screens with precision.
Overview
Fault Code
SPN 111 / FMI 4
Category
Engine Protection
Fault Type
sensor
FMI Category
electrical low
Severity
Medium
Derate Risk
Sometimes
Regen Inhibit
No
Inducement Risk
No
Component Location: Coolant degas/overflow tank — sensor mounted in tank body
Common Symptoms
- Coolant level sensor fault active
- Coolant level warning may be active
- Sensor reading stuck low or at zero
Root Causes
- Coolant level sensor wiring short to ground
- Sensor connector corrosion
- Sensor failure
- Open circuit in sensor supply wire
Full step-by-step tests, DVOM guidance, and pinout data are available inside the AI Diesel Tech diagnostic session.
AI walks you through every test — one step at a time. Plans start at $12.95/mo.
Derate Behavior
Power Derate
Sometimes
Mileage / Regen Notes
Sensor failures common 300k–500k miles. Connector corrosion increases with age.
System Interactions
SPN 111 FMI 4 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
TSB Reference: Cummins TSB 4021531 — Coolant Level Sensor Electrical 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
ISX15: Confirm actual coolant level before replacing sensor.
Detroit
DD15: Check wiring harness routing near hot engine components.
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 4 — 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.
Get weekly diesel diagnostic tips
Real-world fault code walkthroughs, wiring tips, and shop-tested fixes — free.
No spam. Unsubscribe anytime.
Get AI-Guided Diagnosis for SPN 111 FMI 4
The diagnostic engine walks you through every physical test — step by step, on your phone, at the truck. No guessing. No wasted parts.