An automotive O2 sensor or oxygen sensor is used to monitor the richness of exhaust exiting the engine. The O2 sensor activates when the engine exhaust is hot enough to generate a reading. The engine computer reads the sensor's signal and generates an optimal gas-and-air mix for fuel economy. Manufacturers often recommend replacing O2 sensors around 100,000 miles. Vehicles with onboard computers compare the readings from the O2 sensor to the factory settings and will send an error code if there is a discrepancy in the readings. The error code will cause a "check engine" or "O2 sensor" instrument light.
Notice if you are purchasing more fuel than is normal for your vehicle. Fuel economy significantly goes down when the O2 sensor is going bad. This alone is does not make O2 sensor failure a foregone conclusion, as other issues may cause poor fuel economy, such as hose leaks or problems with the ignition or spark plugs, to name a few.
Press on the accelerator when you are in park at idle. If you notice a loss of power, the O2 sensor may be going bad. You may also notice the vehicle misfiring frequently, which leads to a lean reading from the O2 sensor.
Take your vehicle to an auto repair shop. The mechanic will hook up a computer to the car and retrieve the error code to determine if the O2 sensor needs replacing. The computer will send error codes if it recognizes the 02 sensor voltage is consistently below 0.45 volts. Have the mechanic check for other possible causes for the reading before paying for an O2 sensor you might not need.
