What is SPN 91 FMI 2
- SPN 91: Refers to a fault related to the engine coolant temperature sensor, indicating that the ECM is receiving out-of-range temperature data from the sensor.
- FMI 2: Indicates that the signal from the coolant temperature sensor is too low, meaning the ECM is receiving lower-than-expected readings.
Together, SPN 91 FMI 2 signals that the coolant temperature sensor is malfunctioning or the cooling system is not functioning properly, leading to inaccurate engine temperature readings.
Why It Happened
This fault code is caused by:
- Low coolant levels or coolant leaks.
- A malfunctioning engine coolant temperature sensor.
- Wiring issues between the sensor and ECM.
- A thermostat failure that is not properly regulating coolant temperature.
- Contaminated coolant affecting sensor readings.
How to Resolve It
To resolve SPN 91 FMI 2:
- Check coolant levels: Ensure the coolant is at the proper level and top off if necessary.
- Inspect the coolant temperature sensor: Test and replace the sensor if necessary.
- Inspect the wiring: Look for signs of wear, corrosion, or poor connections between the sensor and ECM.
- Test the thermostat: Ensure the thermostat is working properly.
- Clear the fault code: After repairs, clear the fault code and restart the engine to confirm the fix.
How to Avoid Before It Happens
To prevent SPN 91 FMI 2:
- Regularly check coolant levels and inspect the cooling system.
- Perform routine construction equipment maintenance on the coolant temperature sensor and wiring.
- Use Clue to monitor engine temperature data and receive early alerts for sensor failures or cooling system issues.
