What is SPN 4007 FMI 31 & How to Solve It?

What is SPN 4007 FMI 31

SPN 4007 refers to the Diesel Exhaust Fluid (DEF) dosing system, and FMI 31 indicates a condition exists that has triggered the warning but the ECU cannot define it with a specific cause. It’s essentially a generic, undefined abnormal condition related to the DEF system.

Together, SPN 4007 FMI 31 means the aftertreatment system has detected irregularities in DEF injection or performance, but it doesn’t have enough data to pinpoint exactly what’s wrong. This could lead to reduced engine performance or eventual derate if not resolved.

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Why This Happens

This fault typically comes up due to:

• Low-quality or contaminated DEF.
• DEF injector blockage or performance issue.
• Crystallization in DEF lines or injector tip.
• Intermittent wiring or connector problems.
• Incorrect tank level sensor readings.
• Faulty temperature or pressure readings from the DEF system.

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How to Fix It

Start by eliminating the most common causes first, then work toward more specific inspections:

1. Check DEF fluid quality and make sure it meets ISO 22241 standards.
2. Inspect the DEF injector for clogging or crystal buildup.
3. Flush and clean the DEF lines if crystallization is visible.
4. Check wiring and connectors going to the DEF pump, sensor, and injector.
5. Use diagnostic software to look for additional stored or pending codes.
6. If the DEF system appears physically fine, update or reflash the control module.
7. Clear the code and monitor for reoccurrence.

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How to Avoid It Before It Happens

1. Always use certified, clean DEF that’s stored properly.
2. Flush and clean the DEF system periodically, especially in cold climates.
3. Ensure the tank cap is sealed to prevent contamination.
4. Train your operators to report any exhaust system warnings early.