Genuine OEM BMW Lambda Oxygen Sensor, part number 13628595135. This sensor measures the oxygen content in the exhaust gases, providing critical data to the engine control unit (ECU) to optimize the air-fuel ratio for efficient combustion and reduced emissions. It is typically located in the exhaust system before or after the catalytic converter. Genuine OEM oxygen sensors are calibrated to precise specifications, ensuring accurate readings and reliable performance, which is essential for maintaining emissions compliance and optimal engine performance.