What is SPN 5580 FMI 17 & How to Solve It?

What is SPN 5580 FMI 17:

SPN 5580 refers to the DEF Quality Sensor, and FMI 17 indicates that the sensor is reporting a value below the normal range, meaning the DEF is reading as poor quality or overly diluted.

This code signals that the DEF in the tank likely doesn’t meet minimum purity standards. Using low-quality DEF can lead to failed regenerations and eventual derate.

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Why This Happens

• DEF is diluted with water or non-urea additives.
• Expired or contaminated DEF fluid.
• DEF quality sensor is failing or degraded.
• DEF tank was filled from an open or dirty container.
• Sensor wiring is giving low-voltage readings.

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How to Fix It

1. Drain the DEF tank completely and refill with fresh, certified DEF.
2. Inspect the DEF quality sensor and clean if necessary.
3. Replace the sensor if it continues to report low quality on good DEF.
4. Check wiring and connectors for voltage drop.
5. Clear the code and verify normal system performance.

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How to Avoid It Before It Happens

1. Only use DEF fluid from sealed, ISO-certified containers.
2. Store DEF indoors or in shaded areas to avoid contamination.
3. Inspect and test DEF quality during seasonal services.
4. Educate operators on proper refueling practices.

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