Initially, electronic components replaced the mechanical ones to make various systems more reliable. Mechanical control systems, due to the wear of movable parts and imprecise adjustment, were affected by large errors, which are not shown by electronic circuits operating according to constant set-points. Then, a sharp increase in electronisation was associated with the tightening of exhaust gas emission regulations. Progress in some cases is forced by environmental protection, in other ones by market competition. Modern motor vehicles, slow moving vehicles, military vehicles, etc., are the technical systems being constructed using the latest developments in many fields of science, first of all in mechanics and machine engineering, electrical engineering, electronics, information technology, and chemistry. The rapid development of electronics has led to an increase in the number of electronic components in motor vehicles in all systems, starting with an engine, which has been modified first, to comfort and infotainment systems. The paper presents example measurements of sensors and actuators of an engine with Common Rail fuel supply system on the example of Fiat 1.3 JTD MultiJet engine. The measurements were made using various diagnostic instruments, such as a diagnostic tester, a multimeter or an oscilloscope. Sometimes, the reading of error codes with a diagnostic tester itself is not enough and it is necessary to check the signal waveform with an oscilloscope, which has been presented in this paper.