Controller shows E13 and the generator will not run in AUTO mode.

Safety first: Turn the generator OFF and allow it to cool completely. Never open the radiator cap on a hot engine—scalding coolant can spray out.

• Check coolant level: Once cool, remove the radiator cap and verify coolant is at the proper level. Also check the overflow reservoir. Top up with the coolant type specified by Ryobi if low, and inspect for leaks.
• Inspect radiator and fan: Look through the radiator fins for dirt, leaves, or insect nests. Clean gently with low‑pressure water from the back side. Verify the electric fan spins freely and its connector is secure.
• Test fan operation: With the unit running (qualified persons only), observe whether the fan engages as temperature rises. If not, the fan motor, relay, or wiring may be faulty.
• Check temperature sensor: Inspect the coolant temperature sensor and its wiring for damage or corrosion. Replace the sensor if it is leaking or if resistance tests are out of spec.
• Reset and test: After corrections, clear E13 and run the generator under light load while monitoring temperature. Persistent overheating requires professional diagnosis of water pump, thermostat, and head gasket.