All cars manufactured from 1993 include a catalytic converter in there exhaust system. This is designed to reduces the harmful emissions of hydrocarbons, carbon monoxide and nitrogen oxides which get vented into the atmosphere from the exhaust, it does this by converting gases into water vapour and less harmful gases.
The Catalytic converter has a core of ceramics which has hundreds of pores, these pores are coated with powdered catalysts that contain metals such as platinum, palladium and rhodium.
Catalytic converters are very efficient and have a good life expectancy but they still need to be checked periodically for internal and external damage.
Before and after the Catalytic converter there are oxygen or lambda sensor, these sensors monitor the percentage of oxygen present in exhaust gases before and after the catalytic converter and relays this information to the engine management system or electronic control unit (ECU).
Using information obtained from the oxygen sensors the ECU in turn adjusts the air/fuel mixture constantly so that the cleanest and most efficient combustion is achieved under any operating conditions.
If a catalytic converter fails it may be due to a fault in the engine management system (ECU) or Oxygen sensor because they all work together to help to achieve the lowest possible output of dangerous and polluting gases so replacing a failed Catalytic converter may not rectify the problem completely.