SPN 111 FMI 3: Engine Coolant Level Sensor Circuit


SPN 111 FMI 3 is a fault code that indicates an issue with the engine coolant level sensor circuit. This code is commonly found in diesel engines and is used to alert technicians to potential problems with the engine coolant system.


The SPN 111 FMI 3 fault code specifically points to a “Coolant Level Sensor 1 Circuit – Voltage Above Normal or Shorted to High Source.” This means that a high signal voltage has been detected at the engine coolant level circuit. The engine coolant level sensor is responsible for monitoring the coolant level within the system and relaying this information to the electronic control module (ECM).


The effects of this fault code can vary depending on the type of engine. In automotive applications, there may be no immediate impact on performance. However, in marine engines, the lack of engine protection for circuit or sensor failure can pose a risk.


When diagnosing SPN 111 FMI 3, it is important to consider possible causes such as open return or signal circuits in the harness, connectors, or sensor, as well as signal wire shorted to sensor supply or battery voltage. Additionally, verifying the ECM calibration and checking the calibration revision history for applicable fixes is recommended.

Probable Causes

The probable causes of SPN 111 FMI 3 include a faulty engine coolant level sensor, open return circuit in the engine harness, connectors, or sensor, signal circuit shorted to sensor supply or battery voltage, and sensor supply circuit shorted to battery voltage.


In conclusion, SPN 111 FMI 3 is a fault code related to the engine coolant level sensor circuit. Understanding the effects, troubleshooting steps, and probable causes of this fault code is essential for diesel engine technicians to effectively diagnose and resolve issues related to the engine coolant system. Regular maintenance and thorough diagnostics are crucial in ensuring the proper functioning of the engine coolant level sensor circuit.

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