Code 27
Onan
AC Voltage Sense Fault
Generator shuts down; Code 27 displayed indicating voltage sense loss or abnormal AC output
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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
Loose or disconnected voltage sense leads at controller, Open stator winding in alternator, Faulty voltage regulator, Defective control board voltage sense circuit
How to Fix / Troubleshooting
Safety first: High voltage is present inside the generator. Open the main breaker, disable auto-start, and disconnect battery negative before opening covers. Only work inside the alternator if you are qualified.
- Inspect sense wiring: Locate the voltage sense wires from the alternator output to the controller (often small-gauge wires). Check for loose terminals, corrosion, or broken conductors. Reseat connectors.
- Check main output connections: Verify that the main lugs are tight and free of corrosion. Loose connections can cause erratic sensing.
- Test stator windings: With power off and isolated, measure resistance of stator windings per Onan service manual. An open or shorted winding indicates a failed alternator stator.
- Voltage regulator: If windings test good, the voltage regulator may be defective. Inspect its connector and replace with an Onan-approved regulator if necessary.
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Repair Difficulty
Professional Required
5/5
Required Part
Voltage Regulator
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