What is SPN 929 FMI 12 & How to Solve It?

What is SPN 929 FMI 12:

SPN 929 refers to the Engine Coolant Level Circuit, and FMI 12 means the component or system is not responding to command.

This code appears when the coolant level sensor fails to respond or communicate with the ECM, which can lead to false warnings or a failure to detect low coolant levels risking overheating.

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Why This Happens

• Failed or unplugged coolant level sensor.
• Wiring harness damage or corrosion.
• Internal short in the sensor or control circuit.
• Low coolant triggering erratic readings.
• Faulty ECM input response to the sensor.

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How to Fix It

1. Check the coolant level and refill if necessary.
2. Inspect the coolant level sensor and wiring connector.
3. Test the sensor with a multimeter or swap it out for a known good one.
4. Replace the sensor if it fails to respond under test.
5. Clear the code and confirm sensor updates during engine warm-up.

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How to Avoid It Before It Happens

1. Check coolant levels daily and log usage.
2. Inspect coolant level sensors and wiring at each PM interval.
3. Replace aging sensors every few years to prevent failure.
4. Keep sensor areas dry and corrosion-free.

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