What is SPN 3362 FMI 14 & How to Solve It?

What is SPN 3362 FMI 14:

SPN 3362 refers to the Diesel Exhaust Fluid (DEF) Line Heater, and FMI 14 indicates a special instruction — typically used when a fault doesn’t fall into a standard failure type but still requires immediate attention.

Together, SPN 3362 FMI 14 means the system has detected an issue with the DEF line heater circuit that’s not following expected parameters. This can lead to freezing DEF lines, especially in cold weather, preventing proper DEF delivery and causing aftertreatment failure or engine derate.

‍

Why This Happens

This fault is most likely caused by:

• A failed DEF line heater or heating element.
• Broken or shorted wiring in the heater circuit.
• Control module failing to engage the heater correctly.
• DEF freezing in the lines due to lack of heating.
• Poor electrical grounding or damaged connectors.

‍

How to Fix It

Act quickly in cold climates to prevent system freezing:

1. Inspect the DEF line heater for visible damage or cracks.
2. Unplug and examine the connectors for moisture or corrosion.
3. Test for continuity across the heater wiring.
4. Verify that the control module is sending power to the heater.
5. Replace the DEF line heater if the circuit fails continuity tests.
6. Clear the fault code and retest once the repair is made.

‍

How to Avoid It Before It Happens

1. Always check DEF heaters and lines before winter operation.
2. Keep electrical connectors clean and dry to prevent shorts.
3. Replace faulty heaters before cold weather arrives.
4. Monitor DEF system warnings closely and investigate early.