Delphi Oxygen Sensor; Front | ES20088

Oxygen (O2) sensors are emissions control sensors that detect levels of oxygen in an engine's exhaust. When the element inside the O2 sensor heats up, oxygen flowing through the sensor causes the element to create electricity. This electrical current is sent to the engine's computer and converted to an oxygen level reading. Some O2 sensors are equipped with a heating element to speed up the oxygen-sensing process, while others rely on the engine's exhaust to heat them.

O2 sensors are one of the more commonly failed sensors in an emissions control system. Continuous exposure to exhaust temperatures ranging from 300°-700° Fahrenheit over time causes the sensor element to lose its ability to create voltage, making the sensor give incorrect readings. When this happens, the engine computer operates the fuel injectors on preset fault parameters and turns the check engine light on with a fault code. If an O2 sensor behind the catalytic converter fails, the ECM may turn on the check engine light with a fault code for the catalytic converter because the faulty O2 sensor reading gives the appearance that the catalytic converter is not functioning.

Failed O2 sensors will often result in a lack of engine power that is not usually noticed but a decrease in fuel economy, that is. If your check engine light is on and your vehicle is driving normally, you should still have the fault code checked, as it could very well be an O2 sensor that failed and is causing your vehicle to consume excessive fuel.

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