Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or the fuel entering the engine but when information from oxygen sensors is coupled with information from other sources, it can be used to indirectly determine the air-fuel ratio.
They do not directly measure the air entering the engine. They do not directly measure the fuel entering the engine. Oxygen sensors are located in the exhaust stream. It can be used to indirectly determine the air-fuel ratio. Information from oxygen sensors is coupled with information from other sources.