The oxygen sensor is a device located in the engine of your car that determines the mixture between oxygen and fuel. This information is relayed to the fuel control computer, which can then either increase or decrease the amount of oxygen in the exhaust manifold to maximize performance. The sensor is traditionally made out of a ceramic cylinder plated with platinum electrodes inside and out, and a zirconium dioxide tip that creates voltage. The device is protected by a metallic exterior.
The O2 sensor is the only part in the engine that creates its own voltage. It only starts working after it has been heated by the engine to at least 316 degrees C. Newer models have a heating device built into them to heat the device more quickly so it can begin operation. Once it reaches this temperature, the ceramic becomes conductive to oxygen ions. As oxygen ions pass through it, the zirconium dioxide generates an electric charge. The greater the difference between the oxygen in the manifold and the amount outside, the more ions pass through the sensor in an attempt to reach equilibrium, and the greater the charge that is developed. The platinum electrodes accumulate this charge and send it through the wires and to the car's computer, and the computer can then tell from the strength of the charge if the fuel/air ratio is too lean, too rich or just right.
Oxygen sensors last from 30 to 50 thousand miles on average. They can fail prematurely if they become clogged with carbons or contaminated with other chemicals from the engine. Using leaded gasoline in an unleaded vehicle can cause the sensor to fail as it becomes contaminated with lead. Sensor accuracy can be affected by air leaks in the exhaust manifold or by a misfiring spark plug, both of which will cause the sensor to give false readings and possibly damage the engine's performance. Signs the sensor could be failing are poor fuel economy, loss of power, a rougher idle and an increase in emissions. At this point, you will want to test the sensor. Repairing the sensor is very difficult and costly, and the more sensible solution is to replace it outright in the event of failure.
