Disconnect the plug from the thermal switch.
Bridge the two pins of the plug with a piece of insulated wire. If the fan starts, then the thermal switch is faulty, which in this case interrupts the current circuit.
To continue the movement, put a jumper between the contacts. In this case, the radiator fan will constantly work.
To prevent free-hanging wires from causing a short circuit, insulate them with electrical tape or tape.
If bypassing the thermal switch does not help, apply battery voltage directly to the motor terminals.
If the motor does not rotate, it means that it is defective. In this case, the motor needs to be replaced.
Attention: If there is a jumper, it must be disconnected after the end of the movement, otherwise the fan motor will work until the battery is discharged.