Generator shuts down; controller displays AL06 – Underspeed / Underfrequency

Safety first: Place the generator in STOP and isolate battery negative. Remove load from the generator before further testing.

• Check fuel supply: Inspect primary and secondary fuel filters and replace if dirty. Ensure fuel shutoff valves are fully open and there are no kinks in the fuel line.
• Inspect governor or actuator: For mechanical governors, check that the governor lever moves smoothly and the return spring is intact. For electronic actuators, listen for actuator movement during start attempts; no sound may indicate actuator failure or no power.
• Reduce load: If the alarm occurs only under heavy load, the generator may be overloaded. Verify that total kW and kVA are within the FG Wilson set rating. Shed non-essential loads and retest.
• Check speed sensor: Inspect the magnetic pickup and wiring as for overspeed faults. A weak or intermittent signal can cause false underspeed detection.
• Test run: Start in MANUAL with no load and monitor frequency (Hz). If stable, gradually apply load while watching for frequency droop.