What is SPN 5394 FMI 7 & How to Solve It?

What is SPN 5394 FMI 7:

SPN 5394 FMI 7 indicates a fault in the Aftertreatment 1 Diesel Exhaust Fluid (DEF) Tank Level Sensor Circuit. The FMI 7 specifically means that the sensor is reporting higher than expected readings, often due to a malfunction in the sensor or its circuit. This can affect the proper dosing of DEF, which is essential for reducing nitrogen oxide (NOx) emissions through the SCR system.

Why This Happens

• Faulty or failing DEF tank level sensor.
  
• Shorted or damaged wiring in the sensor circuit.
  
• Corroded or loose sensor connectors.
  
• Malfunctioning Aftertreatment Control Module (ACM) misinterpreting the sensor data.
  
• DEF tank overfilled or incorrect DEF fluid levels.
  
  

How to Fix It

1. Inspect the DEF tank level sensor and wiring for visible damage or corrosion.
   
2. Check the sensor connector for tightness and moisture.
   
3. Test the sensor for correct voltage and resistance values.
   
4. Replace the DEF tank level sensor if it is faulty or providing erratic readings.
   
5. Check DEF fluid levels and verify proper fluid type; replace if necessary.
   
   

How to Avoid It Before It Happens

• Regularly inspect the DEF system during routine maintenance.
  
• Ensure connectors are clean and sealed to prevent corrosion.
  
• Monitor DEF tank levels and perform system resets if necessary.
  
• Replace the DEF tank level sensor at recommended intervals.
  

Clue offers preventive maintenance services to monitor DEF system performance and ensure accurate fluid levels, helping to prevent system faults.