Catalytic converters are one of the measures to reduce air pollution and the environment in general. Mass installation of catalytic converters in the EU began in the last decade, and this measure proved quite effective. He is part of the exhaust system in cars and is located as close to the engine for better performance. An important part of the catalyst is a lambda probe, but their main task while reducing noise the treatment of pollutants and gases produced by the internal combustion engine. Gases that purifies are NOx, HC and CO, and they do their work converted to NO2, H2O and CO2. These gases are seeing long-term harmful to the environment and human health. Lambda probe ensures the correct stoichiometric ratio of air and fuel in the cylinder. Gasoline engines have a rich or lean fuel mixture and task of lambda probe is to bring this ratio to the ideal. She manages fuel injectors via ECU. Its appearance is similar to the spark plug on petrol engine and is located at the catalyst. Diesel engine has better efficiency of the lambda probe because the engine produces less emission of CO and HC. Catalysts are working in extreme conditions and their service life is approximately 100 000 km or 5 years of age. There are various damage catalyst because they work in such conditions, but going to the diagnosis, we can easily detect problems. They are produced from different materials and the most durable metal, which is resistant to shocks. They are installed and in diesel engines and adjusted to euro standards with additions of certain chemical products. They were brought to the high level of quality and efficiency. Besides the mentioned measures pollution can be reduced by replacement of old vehicles, better utilization of fuel consumption, increase of conscience in people that are not unduly used means of transport , investing in public transport and of course, the improvement of air purification systems.