The computer system of a personal car has ECU, which is not just a processor but a microcontroller, it contains memory and other parts like a personal computer but minimized. The ECU manages the system in a way that ensures proper operation, safety, reduces fuel consumption, and makes savings. The CPU strength, needed for this kind of system, grows every day because systems become more complex and therefore require more resources. The infotainment system and a multimedia system, like GPS, use most of the memory. Every section of the car has sensors. They keep track of the environment and status of the car and send that information to the ECU. Depending on the given information, ECU will respond. ECU also helps with driving and warns drivers about possible accidents. Data buses are responsible for data communication between ECU and all other parts, and they are improving every day. At the moment, speeds of data buses used to connect the system of the car are up to 10 megabits per second. There are different types of device connections, such as ring topology. For each part to work flawlessly, diagnostics have to be performed to recognize and fix the errors within the system. We have two types of diagnostics, embedded and external. Embedded diagnostics is in the car. It corrects minor faults and ensures the proper work of a car. For significant mistakes that embedded diagnostics cannot repair, external diagnostics is used. It is available in the car services, and it uses SAE J1979 communication. It tracks conditions like signals, data flow, status readiness, failures, and analyzes each car according to its identification number. The concept of a parking system is used for a practical part. This system protects the vehicle against possible collisions with objects around it and provides better usage of the parking area. It is based on the Croduino Basic3, Croatian Arduino platform with the HC-SR04 ultrasonic sensor. Data from the sensor is displayed on the LCD screen.