I have an 01 grand am 2.4l, and when i changed from a manifold to a header my check engine light came on.....here i came to find out it was a bad front 02 sensor(the 1 that plugs into the header)....when go to buy a new 1 does it matter if the sensor is for the front(header) or the back(behind the cat)?let me kno ....thanx.....and do you know where i can get a good deal? thankx