What Is O2 Sensor (Oxygen Sensor)?

Monitors the oxygen content in exhaust gases to help the ECM maintain the optimal 14.7:1 air-fuel ratio (stoichiometric ratio).

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.