The fan can be driven by a drive belt off of the crankshaft or it can be operated electrically. Regardless of the design used, inspect the fan blades for stress and cracks.
Electric fans are also inspected for damage and looseness. If the fan fails to turn on at the proper temperature, the problem could be the temperature sensor, the fan motor, the fan control relay, the circuit wires, or the controller. To isolate the cause of the malfunction, attempt to operate the fan by bypassing the control. On a computer-controlled system, this can be done by using a scan tool to activate the fan. If the fan operates, the problem is probably in the coolant temperature sensor.
It is also possible to check fan function by jumping the fan relay to attempt operating the fan motor. If the fan operates, the relay may be the faulty component; however, additional tests will have to be performed on the control circuit of the relay.
A jumper wire can also be used to jump battery voltage directly to the cooling fan. If the fan motor fails to operate, check for proper ground connections before faulting the motor.
To direct air flow more efficiently, many manufacturers use a shroud. Proper location of the fan within the shroud should be at lease 50 percent inside the shroud. If the fan is outside the shroud, the engine may experience overheating due to hot under-hood air being drawn by the fan instead of the cooler air. If the shroud is broken, it should be repaired or replaced. Do not drive the vehicle without the shroud installed.