i'll just call them, dont worry, thanks tho. if ur saying ur not sure about the rear one, im assuming ur talkin about the O2 sensor on the cat... unfortunately, thats the one i need, and the one ur not sure about, i already changed the one on the header. make sure if its 3 wire, that the O2 sensor on the back is compatible with it.. u gave me the website, thats the most important part i needed