An oxygen sensor is a necessary component of a car's emissions system. All new cars and many older cars have electronic fuel injection systems, in which a computer regulates the amount of fuel delivered to the engine. The computer communicates with sensors throughout the system to determine how much fuel to deliver to the engine, and how frequently.
Usually located in the exhaust manifold, one end of the oxygen sensor detects the levels of unburned combustibles in the exhaust flow, and the other end connects to wiring that relays the information to the computer. The computer then uses the sensor readings to ensure that the engine is being given the right amount of fuel. Too much or too little fuel will change the readings from the sensor, which will prompt the computer to readjust the amounts of fuel being delivered to the engine.
An oxygen sensor will fail periodically. When the sensor malfunctions, important feedback about engine performance will be lost. As a result, the computer that runs the electronic fuel injection system will have no idea how much fuel to deliver to the engine.
Sometimes, this sensor will have a mileage rating, which indicates how long it is expected to last. There are several ways to find this information. A car's owner's manual or shop manual should state the expected lifespan. If these books are not available, the dealership can look up the expected lifespan of an oxygen sensor for a specific car. Many aftermarket auto parts stores have the same information.
In general, the mileage that an oxygen sensor should last depends on when it was made. In an older car, the unheated sensor should last approximately 30,000 to 50,000 miles (about 48,280 to 80,467 km). A first-generation heated sensor can be expected to last 60,000 miles (96,561 km) or more. For newer cars with a second-generation heated sensor, it may last 100,000 miles (160,934 km).
Once the driver knows the mileage rating for the oxygen sensor in his or her car, it is a good idea to keep records of when maintenance is done; if the woner knows when the sensor was last replaced, he or she will know when it should be replaced again. Replacing the sensor regularly helps maintain the car's gas mileage, prevents other related car troubles, and helps prevent failed emissions tests.