Genuine OEM BMW Oxygen Sensor, part number 11781310838. Also known as a Lambda Probe, this sensor measures the oxygen content in the exhaust gases. It is installed in the exhaust system to provide feedback to the engine control unit for optimal fuel mixture and emissions control. This sensor has a metal body with a ceramic element and a wired connector. Genuine OEM oxygen sensors are calibrated for precise measurement, ensuring proper engine performance and compliance with emissions standards.