The main feature of vehicles manufactured these days is general use of advanced electronic technology. Microprocessors are essential components of automotive subassemblies, gradually replacing analog, mechanical and electromechanical solutions. Therefore, the possibility of identification of defects of these subassemblies becomes one of the basic requirements for carmakers. These tasks are performed by Vehicle Diagnostics Systems. They conduct ongoing diagnostic tests, making possible quick detection and location of defects. The defect code is saved in diagnostic equipment memory, from where it can be read by external diagnostic systems.