What does this 2001 Ford Focus check engine code mean? also?

My 2001 Ford Focus throws the error code P0401 "EGR Flow Insufficient" after about 20 minutes of city driving. What is the likely cause of this? What do I need to fix / replace?

I have been having a little problem with the car getting a bit too hot before the fan comes on (could this be related to the above code?). I noticed that the coolant temp. sensor is not plugged in to anything (the sensor that is screwed in to the intake manifold right where the radiator hose meets the engine) but I cannot find a disconnected wire anywhere to reattach to the sensor. Where does the wire that is supposed to be connected to the coolant temp. sensor lead?

Thanks so much.

Joe