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

What is SPN 3362 FMI 14 (CAT):

This Caterpillar-specific fault refers to the DEF Line Heater, and FMI 14 indicates a special condition — typically undefined but tied to operational failure in cold weather.

This code means the DEF heater is either not functioning or not confirming operation, which risks frozen DEF and interrupted dosing.

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Why This Happens

• Heater element damaged or degraded.
• Moisture in connectors preventing current flow.
• ECM not receiving heater feedback signal.
• DEF lines frozen and heater unable to thaw system.

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How to Fix It

1. Test heater element for proper resistance.
2. Check electrical connectors for moisture or corrosion.
3. Run diagnostic to command heater on and verify operation.
4. Replace faulty heater or control module if no response.
5. Clear the code and confirm performance in cold conditions.

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How to Avoid It Before It Happens

1. Pre-test all heaters before winter.
2. Store DEF equipment in above-freezing temperatures.
3. Use dielectric grease to protect exposed electrical connectors.
4. Replace failing heaters before cold weather.

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