Fan always on need help

I have a 99, 70000km astro van. I got the service engine light on after the dealer changed the fuel filter one week ago. I checked with the code reader and found P0440 which is "Evaporative Emission Control System Malfunction". Can this problem caused by changing of the fuel filter ? When I turn the key to on position, I can hear a loud switching sound under the car near the transmission area. Can anyone tell me what the car is doing when the key is at the "ON" position before I start the engine ?
Also the radiator fan always on and there is click, click switching sound from either the Intake Air Temperature sensor or MAF sensor. It is making the clicking switching sound every 10 seconds. It is doing it whenever the engine is start from cold or hot. Can anyone know what is wrong ?

On the code - make sure your gas cap is good and tight.....

The engine service light is gone. I found out there is a hose connected to the canister next to the fuel filter is disconnected by the dealer when he change it.

Amazing how self aware these newer cars/vans/trucks are isn't it?