Controller displays AL04 / Underspeed and generator fails to reach rated frequency
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.
Possible Causes
How to Fix / Troubleshooting
Safety first: Place the controller in OFF, open the output breaker, and disconnect battery negative before fuel system work. Keep fire extinguishing equipment nearby.
- Check fuel level and quality: Verify the day tank or main tank feeding the Kohler-SDMO generator has adequate clean diesel. Drain water from the fuel pre-filter/water separator if fitted.
- Replace fuel filters: Replace the primary and secondary fuel filters with Kohler-SDMO specified elements. Prime the system using the manual priming pump until fuel is free of air bubbles.
- Inspect fuel lines: Check for collapsed, kinked, or leaking fuel hoses between tank, lift pump, and injection pump. Tighten clamps and replace damaged hoses.
- Governor check: On mechanical governors, inspect the governor linkage and springs for damage or misadjustment. Ensure the speed setting screw has not been tampered with.
- Start under no load: Reconnect battery, clear AL04, and start the generator with the output breaker open. Allow it to reach rated speed before gradually applying load.
If the engine cannot reach rated speed with no load, the injection pump or governor may require professional calibration.
Repair Difficulty
Required Part
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