Genuine BMW Oxygen Sensor - 11787836451. Genuine BMW Oxygen Sensor - 11787836451 is a direct replacement for the original factory-installed oxygen sensor. This oxygen sensor accurately monitors the air-fuel ratio in the exhaust system and helps the engine run efficiently. It is designed to provide superior performance and long service life. It is an OEM quality part that is designed to meet or exceed factory specifications for fit, form, and function.