Controller displays 'Overvoltage' and shuts down the generator shortly after start; AC output measures significantly above nominal (e.g., >260 VAC on 240 V system).

Safety: Open the main line circuit breaker on the generator and the transfer switch. Never work on live AC circuits. Use a properly rated multimeter.

• Verify engine speed: Observe engine RPM with a tachometer. Generac standby units typically run at 3600 RPM (60 Hz) or 3000 RPM (50 Hz). If RPM is too high, inspect the mechanical governor linkage and throttle plate for binding or misadjustment.
• Inspect voltage regulator connections: Locate the Automatic Voltage Regulator (AVR) in the control compartment. Check all plug connectors and sensing leads for corrosion, looseness, or damage. Reseat connectors firmly.
• Measure line voltage: With the generator in MANUAL and no load connected, measure L1–L2 and L1/L2 to neutral. If voltage is still high, the AVR is likely defective. Replace the AVR with the correct Generac part number for your model.
• Check control board sensing: If voltage at the generator terminals is normal but the controller still reports Overvoltage, inspect the low-voltage sensing harness from the stator to the control board. Replace the control board if sensing circuits are faulty.