What Is O2 Sensor (Oxygen Sensor)?

Reports exhaust oxygen or air-fuel information, depending on sensor type, to support mixture control and monitor operation. Stoichiometry is approximately 14.7:1 for conventional gasoline by mass; fuel blends and operating targets differ.

Most vehicles have upstream (before catalytic converter) and downstream (after catalytic converter) O2 sensors on each exhaust bank. Upstream sensors help regulate the fuel mixture in real-time, while downstream sensors monitor catalytic converter efficiency. Faulty O2 sensors commonly trigger codes like P0130-P0167.