What is SPN 3516 FMI 1 & How to Solve It?

What is SPN 3516 FMI 1:

SPN 3516 relates to the DPF Differential Pressure Sensor, and FMI 1 means the value is below normal operating range.

This can interfere with regen scheduling and may falsely signal an empty or unrestricted filter.

‍

Why This Happens

• Pressure sensor tubing disconnected or leaking.
  
• Sensor failing or reading zero pressure.
  
• Exhaust leak before or after DPF.
  
• ECM not receiving accurate pressure data.
  

‍

How to Fix It

1. Inspect and reconnect all pressure sensor lines.
   
2. Replace or clean the sensor if values remain low.
   
3. Check for exhaust leaks around the DPF.
   
4. Run a regen and verify pressure rise.
   
5. Clear the code and recheck pressure response.
   

‍

How to Avoid It Before It Happens

1. Clean sensor tubing regularly.
   
2. Replace sensors at recommended service intervals.
   
3. Monitor regen pressure values consistently.
   
4. Track DPF backpressure against mileage or hours.