cooling fans not coming on

The cooling fans receive a signal to turn on depending on coolant temperature sensor data provided to the engine's computer. The cooling fan motors operate with an on board controller. You could have a faulty relay, but likely the motors themselves are the cause of failure. A diagnostic tool should be utilized to check for the actual temperature reading (in the event it never reaches high enough to turn the fans on) and can be used to see the fans commanded to be turned on and off. Testing should be done while this is happening to see if there is power to the fan as commanded and as a result see if the motors are failed.