What is SPN 629 FMI 8 & How to Solve It?

What is SPN 629 FMI 8:

SPN 629 FMI 8 indicates a problem with the Engine Coolant Temperature Sensor Circuit. FMI 8 suggests that the sensor is sending an invalid signal, potentially due to a low voltage condition, affecting the ability of the ECM to accurately monitor engine coolant temperature, which could lead to engine overheating or inefficient performance.

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Why This Happens:

• Faulty coolant temperature sensor.
  
• Damaged or shorted wiring in the sensor circuit.
  
• Corroded or loose sensor connectors.
  
• Low coolant levels, causing inaccurate readings.
  
• ECM failure to interpret the sensor’s signal.
  
  

How to Fix It:

1. Inspect the coolant temperature sensor for physical damage or wear.
   
2. Test the sensor’s voltage and resistance to ensure proper functionality.
   
3. Check the wiring and connectors for damage, corrosion, or loose connections.
   
4. Replace the faulty coolant temperature sensor if necessary.
   
5. Ensure that coolant levels are correct and the cooling system is functioning properly.
   
   

How to Avoid It Before It Happens:

• Regularly inspect the coolant temperature sensor and wiring.
  
• Keep connectors clean and free from corrosion.
  
• Maintain proper coolant levels and replace coolant as needed.
  
• Perform diagnostic checks to ensure sensor accuracy.
  
• Clue’s Equipment Maintenance services help monitor coolant system health and ensure the proper functioning of temperature sensors before issues arise.