In the good old days, cars weren’t all that different from bicycles. Everything was controlled manually through pedals and cables and there were only a few meters of electrical wires for lighting and starting.
Nowadays, things are very very different! The steering wheel doesn’t “steer” – it is a sensor which sends signals to a computer controlling a motor which turns the wheels. It is the same story with all the other pedals, knobs, and levers in the car. Modern cars are made up of 40 or more computer modules which talk with each other over several different internet connections. These computer modules monitor and control every aspect of the car’s operation, from headlights (HCM), steering wheel (SWM), brakes (BCM), engine (ECM) and many many more. Each module gathers information from a multitude of sensors, processes this information and then makes decisions and carries out control actions. A 1960’s car did not have a single electronic part (except for the radio). Cars now are made up of millions of transistors in thousands of components in hundreds of sensors and computer modules. Putting each one of the millions of transistors to work is the job of the 100 million lines of computer programming code that are found in cars now.
What could possibly go wrong? Everything! If even one of the millions of transistors and other electronic components fails or the messages on the internet become distorted or blocked, the entire system and even the entire car could stop working. Fortunately, many of those 100 million lines of computer programming are devoted to detecting problems and warning the driver but the ability of the computer module to accurately diagnose most problems is limited. A missing measurement, from an wheel speed sensor for example, might be the result of a broken sensor, bad wiring from the sensor to the computer module, a broken computer module, or all too often, dirt or rust on the sensor.
Car diagnosis has always been like the practice of medicine. One listens to the patient’s complaints, examine their symptoms, perform tests to identify the source of the problem and finally, treatment. What is different now is the entire nature of the “problem”. How cars work is not related to bicycles anymore – the design of modern automobile systems is virtually identical to airplanes, nuclear power plants, and coffee machines.
