I had the same problem with my front sensor. I bought a Universal Bosch O2 sensor and replaced it myself. It's a little tricky to install, you have to splice wires, and there's not a lot of room under the car. It's easier to unplug the sensor. I couldn't get the plug connector out on mine. Anyway, the universal sensor was only $100 Canadian as opposed to $250 for the “real” sensor. It works just fine. I can't remember the part number off hand, but the parts store cross referrenced it to the non-universal one.