Rendy, If the 02 sensor is approaching 30,000 miles, it's due to be replaced. Also, if you car has been running rich. The the fuel system may lean out after replacing it 02. Also, after replacing the o2 sensor, the Air flow meter may have to be adjusted to get the correct reading. I adjust by ear and am usually right on the money, but trying to find someone with the right equiptment might be a challenge. I also have Cat's in stock at a savings.You can see on the web site. And , no they don't last forever. John hervey http://www.specialtauto.com/engine.shtml