What is SPN 639 FMI 12 & How to Solve It?

What is SPN 639 FMI 12:

SPN 639 is a CAN communication fault, and FMI 12 means the module or system is not responding to a data request.

It typically appears when a connected module (like DEF or VECU) goes offline or resets unexpectedly.

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Why This Happens

• Power loss or poor ground at module.
• Network connector corrosion.
• Control module failure or reboot.
• Damaged CAN wiring or noise interference.

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How to Fix It

1. Use diagnostics to identify the silent module.
2. Inspect connectors and voltage supply.
3. Test for proper network resistance (should be 60 ohms total).
4. Reflash or replace module if non-responsive.
5. Clear the code and verify consistent communication.

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How to Avoid It Before It Happens

1. Secure wiring from pinch and heat damage.
2. Replace worn connectors or oxidized terminals.
3. Document module reboots or resets.