I have just replaced the CS sensor on my megane and it is relativly easy to get to and change. Follow the line of your HT leads to the righ of the engine. Drop down the side casing about 3 inches and it should be there. Two 10mm bolts either side, undo the wire and hey presto! I paid £29.94 for a new sensor from most autofactors. Hope that helps!
Chris, April 2008