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What are the symptoms of a bad oxygen sensor?

The biggest indicator of a faulty oxygen sensor is a noticeable decrease in fuel economy, along with a rich mixture. Now, this does not automatically indicate that the sensor has failed. Be sure to check all vacuum hoses for leaks as well as the ignition system, check the plugs, (are they fouled?) check the rotor, distributor cap, points, spark plug leads, and condenser (check all of these where applicable) Vacuum leaks and ignition problems are notorious for causing fuel economy problems. It’s a good idea to inspect and re-new the vacuum hoses every couple of years anyway. Other symptoms of a faulty sensor are a loss of power, (particularly when accelerating from a stand-still), overheating, and spark plug fouling, both of these are due to an increased rich or lean running condition.

Most modern cars nowadays come with sort of a built in troubleshooting guide that can help you diagnose if the sensor is bad. There is usually a port or connector where you can plug in a computer and extract codes from the fuel injection computer. In the case of most new cars, when an error occurs, it generates a code and stores it. Using the computer, you can extract the code from the fuel injection computer. This is invaluable in determining not only a bad oxygen sensor, but all sorts of other problems as well. In many cases, this can tell you if the sensor is bad, however if it does not, keep reading, the steps below will go over how to test the sensor.