What is SPN 5055 FMI 17 & How to Solve It?

What is SPN 5055 FMI 17:

SPN 5055 refers to a DEF system performance issue, and FMI 17 means the sensor is reporting below normal operating range.

This often indicates the DEF pressure, dosing, or temperature is too low, disrupting emissions control and triggering derate.

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Why This Happens

• DEF pump failing to build pressure.
• Frozen or restricted DEF lines.
• The dosing valve stuck closed.
• DEF heater not activating.

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How to Fix It

1. Inspect DEF lines, pump, and dosing valve for blockage.
   
2. Test DEF pressure and flow during engine operation.
   
3. Warm up the system and verify heater function.
   
4. Replace the DEF pump or valve if unresponsive.
   
5. Clear the code and confirm pressure and dosing are within range.
   

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How to Avoid It Before It Happens

1. Run DEF system tests before cold weather season.
   
2. Use DEF with proper storage and handling.
   
3. Keep lines and fittings clean and protected.
   
4. Schedule heater and pump replacements based on usage.