OK they are needed for the engine to run at the right mixture, it is what the computer makes its final adjustments with. If the are shot you will probibly notice a drop in fuel economy also. I would clear the computer then if they show again have them changed, I know they are not cheep but it is worth it.
I did the one in my NX not long back. $70 for a nice one but I think my fuel milage increased by 3 or 4 miles per gallon of gas.