Drain the liquid from the cooling system to a level corresponding to the lower edge of the thermostat housing.
Disconnect the connector and remove the thermal switch.
Place the thermal switch in a container of hot water. At water temperatures up to 90°C, the thermal switch contacts must be closed. Heat the water, the thermal switch contacts should open before the water boils. If both tests are negative, replace the thermal switch.
When replacing the radiator fan thermal switch, be sure to install the O-ring, otherwise coolant may leak.
Add liquid to the cooling system to the required level.