The ability of the Volkswagen oxygen sensor to detect and analyze the amount of oxygen in the exhaust gases is how the onboard computer knows what the air to fuel ratio should be. The actual data that is being transferred to the onboard computer from the oxygen sensor is the ratio of oxygen in the exhaust gases as compared to the oxygen levels in the atmosphere currently surrounding the Volkswagen. It is true that even when the elevation the vehicle is traveling is changing the levels of change in the oxygen levels are minute, but it does matter. This is how precise the calculations are in the manner of which your engine operates at. And when you notice the check engine light illuminated on your dash board, its source should always be investigated as soon as possible. A failing Volkswagen oxygen sensor is one of the reasons for the check engine light to go on. It will also turn on if just the wire to the oxygen sensor is disconnected or damaged. A visual inspection of this sensor in your exhaust pipe can determine if it is the sensor or the wire on your Volkswagen. Once the codes are retrieved from the onboard computer, the owner of the vehicle will know if the faulty sensor is the oxygen sensor. If it is then the first thing that should be done once a replacement part is obtained is the disconnecting of the battery. This will not only make it safe to handle the electrical wires on your Volkswagen but it will also clear the memory of the onboard computer so a faulty reading of a failing oxygen sensor will not appear once the new one is in place.