E04
Yamaha
Underspeed / Underfrequency Fault
Generator shuts down during run and displays E04 on the Yamaha standby controller.
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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 fuel starvation, Clogged fuel filter, Weak governor spring or faulty governor actuator, Heavy load exceeding generator capacity
How to Fix / Troubleshooting
Safety first: Turn the generator OFF and disconnect the battery negative cable. Isolate the generator from the building load using the transfer switch before troubleshooting.
- Check fuel supply: Verify that the fuel shutoff valve is fully open. For LPG/NG units, ensure gas supply valves are open and the regulator is not iced or blocked. For diesel, confirm there is adequate fuel in the tank.
- Inspect and replace fuel filter: Locate the primary fuel filter/water separator and any inline filters. If they appear dirty or have not been changed per schedule, replace them with Yamaha-specified filters and prime the system.
- Reduce load: With the generator running in MANUAL, gradually add loads. If E04 occurs only under heavy load, the total demand may exceed the generator's rated kW. Rebalance or reduce loads on the transfer switch circuits.
- Check governor operation: Observe the throttle linkage while the unit is running. If it hunts or fails to open under load, the governor actuator or spring may be weak. Inspect for binding linkage and replace worn parts.
- Controller reset: After corrections, clear the E04 code and perform a full-load test while monitoring frequency (should remain near 50/60 Hz as specified).
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Repair Difficulty
Medium
3/5
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