Safety: Isolate the generator from the building load before testing. Disable automatic start.

Reduce load: Open the main generator breaker and any large motor loads (HVAC, pumps). Attempt to run the generator with no load to see if it maintains rated speed.
Check fuel system: Inspect fuel filters, lines, and valves for restrictions. Replace clogged fuel filters and ensure gas pressure (for NG/LP) meets CAT requirements.
Inspect governor linkage: Verify that the mechanical or electronic governor linkage moves smoothly and is not binding. Tighten any loose linkages.
Verify speed sensor: As with overspeed faults, inspect and test the engine speed sensor and wiring.
Gradually reapply load: If the generator holds speed at no load, slowly add loads while monitoring frequency. Avoid exceeding the generator's rated kW.

Persistent underspeed under normal load suggests a governor or engine power issue that should be evaluated by a CAT technician.

Generator shuts down, E-08 displayed, no AC output to load

Possible Causes