To maintain a proper air to fuel mixture in your engine, it is important that the oxygen sensors are working properly. If there is a sudden high fuel consumption or issues with starting the car, chances are you need your O2 sensor checked. Replacing your oxygen sensor is an inexpensive maintenance but if left unchecked, emissions, engine performance and fuel efficiency will suffer. If ignored long enough, the catalytic converter can be damaged and might need to be replaced. A faulty O2 sensor, may cause a rough idle, but isn’t a big safety concern. From an environmental point of view, a new Oxygen sensor will not only save gas, but also reduce air pollution.An oxygen or (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.