If you want you can try just replacing the front one and make sure you put the adapter harness in with it. Part of the problem they've been having is not only bad sensors but the harness is also failing. The O2 sensors of old had a simple vent right in the back of the sensor so they could get their reference air in that way. The new ones are supposed to draw air in through the harness itself. It is actually supposed to pull it in through the space around the copper wires under the plastic sheathing. The word I got was that the coating on the wires was contaminating the reference air and causing screwy readings so they put in a new sensor and the adapter was supposed to adress the contamination being caused by oil leaks and the like. It could all be smoke and mirrors but the new sensors and adapters do seem to work. The dealership is only really concerned with two things, turning a profit and fixing your car right the first time. You have codes for both, they have an on going problem with O2 sensors, this dictates that you need both and you probably do. If you want to do it yourself then you can take the gamble and stuff just a front in and see what happens. Just remember to get the adapter harness with it as well.

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