AL25
Kohler-SDMO
Underfrequency Protection Trip
Controller shows AL25 / Frequency Low and load is shed
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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 unable to maintain speed under load, Excessive load applied, Fuel restriction, Governor response too slow
How to Fix / Troubleshooting
Safety first: Disconnect non-essential loads and open the generator breaker before troubleshooting.
- Check load level: Compare total connected kW to generator rating. Remove large motor or heating loads and retest.
- Fuel system: Inspect and replace clogged fuel filters, check fuel level, and ensure fuel lines are not restricted.
- Governor response: Inspect governor linkage for free movement. On electronic systems, verify droop/isochronous settings per Kohler-SDMO specs.
- Test no-load frequency: Run the generator with no load and adjust speed to nominal frequency if necessary.
- Reset alarm: Clear AL25 and gradually reapply load while monitoring frequency.
Persistent underfrequency under rated load may indicate engine wear or injection issues requiring professional service.
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Repair Difficulty
Hard
4/5
Required Part
Fuel Filter Set
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