F12
MTU Onsite Energy
Generator Overfrequency
Controller displays F12 – Overfrequency alarm/shutdown
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Engine overspeed, Incorrect governor speed setting, Faulty speed sensor, Controller frequency scaling error
How to Fix / Troubleshooting
Safety first: Do not operate the generator with frequency outside specification. Isolate from load.
- Measure frequency: Use a frequency meter to confirm the actual output frequency at the generator terminals.
- Check speed setpoint: In the MTU controller or governor module, verify that the rated speed (e.g., 50/60 Hz) is correctly configured.
- Inspect speed sensor: Check the engine speed sensor for proper mounting, cleanliness, and wiring integrity.
- Governor adjustment: If the engine is running too fast, adjust the governor speed setting according to MTU procedures. Do not exceed rated speed.
- Test under load: After adjustments, clear the F12 alarm and test with gradual load application while monitoring frequency.
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Repair Difficulty
Medium
3/5
Required Part
Electronic Governor Actuator
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