* Faulty coolant temperature sensor: The coolant temperature sensor is responsible for sending a signal to the engine control module (ECM) when the engine coolant temperature reaches a certain level. If the sensor is faulty, the ECM will not receive the signal and will not turn on the fans.
* Faulty fan relay: The fan relay is responsible for supplying power to the fans. If the relay is faulty, it will not be able to supply power to the fans and they will not come on.
* Faulty wiring: The wiring between the coolant temperature sensor, the ECM, and the fan relay may be damaged or disconnected. If the wiring is damaged, the ECM will not receive the signal from the sensor and will not be able to turn on the fans.
* Faulty fan motor: The fan motor may be faulty and unable to turn the fans.