The coupling on the rear 02 sensors is different from the front. You can interchange the rears.I just replaced my front 02 sensors and the dealership gave me the rears for the front and the do not work. I had to go back to the dealer three times until they finally gave me the right part number, some of the fronts have the part number mixed up on the senors. The front sensors have gray caps and the rear have black caps the rears have the female to male coupling on an angle. Hope this helps.
