I have a 2002 S60 non turbo. I have put 2 sets of oxygen sensors in it in 2 months. They are aftermarket sensors. Initially I got a code saying the back sensor was bad S2B1 so I replaced it almost immediately it said the other sensor S1B1 was bad so I replaced it as well. Now this has happened twice in pretty much the same way and now after a few weeks of use the front sensor is saying voltage too high... Any help to solve this problem permanently would be Greatly appreciated. Also the car has 199500 miles on it.