A BMW oxygen sensor is one of the many types of input devices that feed the computer of your vehicle with the vital information required for a smooth ride and operation of your car. The oxygen sensor is connected to the fuel system of your car to provide information that will be used for determining the correct fuel to air ratio that is used for the best possible performance of your engine. It is also used for the best possible mileage for an increase in fuel efficiency. The specific function of the oxygen sensor on your BMW is to compare the levels of oxygen in the atmosphere around your vehicle with what is present in the exhaust gases being produced by your engine. The reason this is done is so no matter what elevation you are at, the correct concentration can be determined by the oxygen sensor so your BMW will perform as you expect it too. Every year the technology of this type of emission sensor changes, and is the reason for new styles of BMW oxygen sensors from year to year even on the same models. This allows for improvements in how fast and accurate the sensor completes is assignment when called upon to do so when the engine is running. If the oxygen sensor that is attached to the exhaust system on your BMW ever fails or malfunctions the check engine light will come on that is located on your dash. Your computer will store in its memory just what error has occurred and it can be retrieved from the computer as a code number. Not only does your technician have a list of what each code refers to but there are also many car manuals that have a complete list for the vehicle owner that wishes to work on their car themselves.