E12
Yamaha
AC Undervoltage / Loss of Excitation
Generator shuts down and displays E12 during operation.
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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
Failed AVR, Open field winding in alternator, Loose excitation wiring, Shorted rotor or stator windings
How to Fix / Troubleshooting
Safety first: Disconnect the generator from the load and turn OFF the unit. High currents may be present; only proceed if you are comfortable working around electrical equipment.
- Measure AC output: Start the generator in MANUAL (if it will run) and measure output voltage. If very low or zero, suspect excitation issues.
- Inspect AVR and wiring: Open the alternator terminal box. Check the AVR connections and field leads for looseness or burns. Tighten or replace damaged connectors.
- Test field winding: With the engine off and battery disconnected, measure resistance of the rotor field winding at the slip rings. Compare to Yamaha specs. An open or shorted reading indicates a bad rotor.
- Replace AVR: If the field winding tests good but there is no excitation, replace the AVR.
- Professional repair: If rotor or stator windings are defective, the alternator will need professional rewinding or replacement.
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Repair Difficulty
Professional Required
5/5
Required Part
Alternator Rotor / Field Winding
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