The impact of the exhaust system quality on the exhaust gases testing was analized in this Masters thesis in both Otto and Diesel engines. By working at a vehicle inspection station an observation has been made considering linking exhaust system faults with the result od the exhaust gases testing. The theoretical part of the Master thesis deals with themes considering high temperature corrosion in the exhaust systems and the description of the materials used in manufacturing exhaust systems and parts related to them. The experimental part of the Master thesis deals with analysis and the comparison of vehicles with correct exhausts and the ones with faults in their exhaust systems. The examination was conducted in Croatian Vehicle Center's Vehicle inspection station Donji Miholjac by working as a vehicle inspection supervisor. All data used in the thesis was anonymous and used only for a statistical data comparrison without the vehicle owners data and the vehicles VINs. The conclusion was that the faults in exhaust systems can have both positive and negative impact on vehicle exhaust gases examination. Vehicles with an Otto engine that have faults in their exhaust system have a raised oxygen levels resulting in raised λ factor and failing the examination while vehicles with Diesel engines leak the exhaust gases so the minority of gases go to the exhaust pipes into the examination machine so the examined levels seem better than what they would be in exhaust systems without faults.