The oxygen sensor (or 02 sensor or lambda sensor) has a main role in the reduction of polluting gases. The sensor is in charge of collecting and transferring to the engine information about the variation of the volume of oxygen contained in the exhaust gases. This prevents the vehicle from controlling the mix of air and gas and avoids excess or lack of gas. The O2 sensor also contains platinum, a precious metal which resists to high temperatures. Most recent manufactured sensors can reach a rate of purification as high as 98%.
For the history, the first O2 sensor was introduced in 1976 on a Volvo 240. California vehicles got them next in 1980 when California's emission rules required lower emissions. Federal emission laws made O2 sensors virtually mandatory on all cars and light trucks built since 1981.