An oxygen (O2) sensor is an electronic device in your exhaust system that measures the air-to-fuel ratio in your engine. By sensing the amount of oxygen in the exhaust, it helps the engine adjust the amount of fuel that it consumes. To maintain a proper air to fuel mixture in your engine, it’s important the oxygen sensors are working properly. If you have sudden high fuel consumption or issues starting the car, chances are you need your O2 sensor checked. Replacing your oxygen sensor is an inexpensive procedure. If left unchecked, your emissions, engine performance and fuel efficiency all will suffer. If ignored long enough, the catalytic converter can get damaged and might need to be replaced. A faulty O2 sensor can cause a rough idle, but it’s not a big safety concern. From an environmental point of view, a new O2 sensor will not only save gas but reduce air pollution.