Oxygen sensors, also known as O2 sensors​ or lambda sensors, are critical components in a vehicle's engine management system. They monitor the oxygen content in the exhaust gases, providing real-time data to the Engine Control Unit (ECU). This data allows the ECU to adjust the air-fuel mixture for optimal combustion, maximizing fuel efficiency, reducing emissions, and ensuring engine performance.
Modern vehicles typically have at least two oxygen sensors: one upstream​ (before the catalytic converter) and one downstream​ (after the catalytic converter).