If there's no damage apparent to the wiring or connector remove them and clean them, I use aerosol cat cleaner and toothbrush or similar! Yep, one in front of each cat and one behind. If you have on OBD 2 reader it might tell you which one it is, certainly you'll get the side it's on. Buy yourself a proper lambda sensor spanner as the sensors are easily damaged, spanner not expensive on the Bay! Lambda sensors are! Use penetrating oil first and leave overnight. If it's still to tight use some heat at the threads on the exhaust itself and when hot try again it should then undo. watch the wiring when applying heat and obviously any other issues that could cause damage or fire risks! Lambda sensors are colour coded and the front and rear are different. It is possible that one has failed but usually it's dirt or wiring issues on these low milage cars. And they sit right in the wheel arches!
