The front Oxygen Sensor (O2 1) is located in the exhaust manifold, which aims to detect the amount of oxygen in the exhaust gas compared to the outside air. This sensor consists of a zirconia ceramic tube, which is closed at one end. The material (zirconium) allows the voltage to be approximately 1V under rich conditions, and under poor conditions of 0V.
The front Oxygen Sensor (O2 1) sends a signal to the ECM (Engine Control module), which it uses to adjust the duration of the injection pulse and thus makes the air-fuel ratio ideal. This ideal ratio regularly occurs near the radical change from 1V to 0V.