GM Genuine Parts Oxygen (O2) Sensors are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These sensors are special feedback sensors on your vehicle's exhaust system and measure the proportion of oxygen in exhaust gases. Using this measurement, the engine control module (ECM) can adjust the air/fuel ratio to near the optimal value of 14.7:1. At this ratio, engine performance, emissions, and fuel economy are all optimized. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).