What is SPN 3480 FMI 2 & How to Solve It?

What is SPN 3480 FMI 2:

SPN 3480 FMI 2 indicates a fault with the Diesel Exhaust Fluid (DEF) Tank Level Sensor Circuit – Voltage Below Normal. This means the engine control module (ECM) is detecting a lower-than-expected voltage signal from the DEF tank level sensor, which monitors the DEF fluid level critical for emissions control.

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Why This Happens

Common causes include:

• Faulty DEF tank level sensor.
  
• Damaged, corroded, or loose wiring/connectors.
  
• Low DEF fluid level triggering sensor alert.
  
• Faulty ECM or sensor calibration issues.
  
  

How to Fix It

To resolve this fault:

1. Check the DEF fluid level and refill if low.
   
2. Inspect the DEF tank level sensor and wiring for damage or corrosion.
   
3. Test the sensor voltage output and replace if faulty.
   
4. Repair or replace damaged wiring or connectors.
   
5. Clear the fault code and monitor DEF system status.
   
   

How to Avoid It Before It Happens

Prevent this fault by:

• Regularly monitoring and maintaining proper DEF fluid levels.
  
• Inspecting the DEF tank level sensor and wiring during routine service.
  
• Using high-quality DEF fluid to avoid sensor contamination.
• Use Clue’s Asset Tracking to monitor the DEF tank sensor's performance in real-time and catch issues with voltage levels before they affect emissions control.