Southampton Audi Audi glossary

Unlike the oxidising catalytic converter, the three-way catalytic converter can oxidise and break down gases and also convert oxides of nitrogen into environmentally more compatible nitrogen and oxygen as well as convert hydrocarbons and carbon monoxide. The combined process of these conflicting chemical reactions requires continuous control inasmuch as the exhaust may only contain the amount of oxygen that is required for the oxidation process (otherwise the reduction process will be impaired). For this reason, modern cars are always equipped with closed-loop, three-way catalytic converters. In contrast to the open-loop type, they have an oxygen sensor or “lambda probe” that measures the residual oxygen content in the exhaust. Based on this parameter, the electronic engine management system adjusts the fuel-air ratio to assure efficient exhaust clean-up.