The working principle of the oxygen sensor is based on the conductivity of oxygen ions. Inside the sensor, there is an electrolyte membrane, usually made of stable zirconia material, coated with different metal electrodes on both sides. One side comes into contact with the exhaust gas inside the exhaust pipe, while the other side is exposed to the atmosphere. When the oxygen concentrations on both sides differ, oxygen moves through the electrolyte membrane, creating a voltage difference, which is directly proportional to the oxygen concentration difference in the gas. This voltage difference is converted into an electrical signal by the internal circuit, reflecting the air-fuel ratio status of the mixture. This characteristic of the sensor allows it to serve as a key component in the automotive emissions control system.