What is SPN 3362 FMI 7 & How to Solve It?

What is SPN 3362 FMI 7:

SPN 3362 refers to the DEF Line Heater, and FMI 7 means the system has detected mechanical or electrical degradation.

The heater may not reach or maintain the correct temperature, risking frozen lines and dosing failure.

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Why This Happens

• Aging heater unable to maintain operating range.
• Internal electrical resistance rising.
• Control circuit partially shorted or overheating.
• DEF crystal buildup interfering with heater contact.

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How to Fix It

1. Test the heater circuit for correct resistance and current draw.
2. Inspect DEF lines for freezing or poor insulation.
3. Replace heater if resistance is out of spec or function is degraded.
4. Clear the fault and test DEF flow in cold startup.

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How to Avoid It Before It Happens

1. Replace DEF heaters every 2–3 winters in cold regions.
2. Insulate lines and fittings near heater elements.
3. Monitor real-time DEF heater output during operation.