An oxygen sensor may get damaged due to normal wear and tear. However, over time, carbon deposits may build up over the sensors, preventing them from functioning properly. The sensor can also become contaminated with silicon content from the coolant or anti-freeze. When the oxygen sensor begins to fail, it will exhibit symptoms such as; rough engine idling, poor fuel economy, increased emissions and misfiring of the engine. Having your oxygen sensor regularly cleaned for impurities can ensure their proper function. Some cars have a special O2 sensor light on their dashboard that indicates when to check the oxygen sensor. Unheated sensors usually last 30,000 to 50,000 miles, while newer oxygen sensors need to be replaced at about 100,000 miles however, it should be checked at regular intervals to ensure that it is working properly (approx. every 30,000 km).