What is SPN 3516 FMI 2 & How to Solve It?

What is SPN 3516 FMI 2:

SPN 3516 refers to the Aftertreatment Diesel Particulate Filter (DPF) Pressure Sensor, and FMI 2 means the sensor is reporting erratic, intermittent, or incorrect data.

This fault appears when the ECM cannot trust the pressure readings used to trigger and monitor DPF regeneration, which can delay regen or cause it to fail.

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Why This Happens

• Sensor wiring intermittently losing connection.
• Pressure sensor beginning to fail.
• Loose or cracked pressure tubing.
• Debris or soot blocking sensor hose.
• Electrical noise interfering with signal.

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How to Fix It

1. Inspect the sensor and tubing for cracks, soot buildup, or leaks.
2. Test the wiring harness for voltage stability.
3. Replace the sensor if resistance or signal output is unstable.
4. Secure all connections and retest during regen.
5. Clear the code and monitor pressure behavior under load.

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How to Avoid It Before It Happens

1. Clean or replace sensor tubing regularly.
2. Mount sensor wiring away from heat sources and vibration.
3. Run regen tests during major inspections.
4. Replace DPF pressure sensors proactively before 5,000 hours.