The fan is controlled by your engine control module. The coolant
temperature is reported to the engine control module by the coolant
temperature sensor in the thermostat housing.
Before jumping into further repairs, you should make an audit of your
cooling system's performance.
First, check your coolant level. If low, check for and repair any leaks.
Next, check for proper coolant flow. With the engine cold, remove the
radiator cap and start the engine (a/c off). You should see the coolant
circulate through the radiator prior to the fan turning on and prior to
coolant boiling out of the radiator. If not, you have something
preventing flow. In most cases, this is caused by a stuck thermostat,
can also be caused by a clogged radiator. If you have trouble seeing
enough into the radiator to tell whether you have coolant flow, you can
feel the hoses. If only one hose is hot, the coolant is not flowing. If
both hoses are hat, the coolant is flowing.
Once you've determined you have coolant flow, allow the engine to
to run. The radiator fan should begin to cycle on and off as necessary
manage coolant temperature. It should continue doing this without the
coolant boiling out of the radiator.