F27
MTU Onsite Energy
Starter Crank Release Failure
Controller displays F27 – Crank disconnect failure, starter remains engaged
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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
Sticking starter solenoid contacts, Faulty crank relay, Controller output stuck on, Wiring short in crank circuit
How to Fix / Troubleshooting
Safety first: A starter that remains engaged can be severely damaged. Immediately stop the engine and isolate DC power.
- Inspect starter solenoid: Check for signs of overheating or welded contacts. Replace the solenoid if it does not release properly.
- Check crank relay: Test the crank relay in the control panel for sticking contacts. Replace if necessary.
- Controller output: Verify that the MTU controller is not continuously energizing the crank output due to a configuration or hardware fault.
- Wiring inspection: Look for shorts between the crank control wire and a DC source.
- Functional test: After repairs, clear the F27 alarm and perform a start/stop test, confirming that the starter disengages promptly after engine start.
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Repair Difficulty
Hard
4/5
Required Part
Starter Solenoid
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