When the Citroen c5 engine control system fault light comes on, it means that the ECU is damaged. The ECU is the engine's regulating computer. The ECU is called the brain of the engine. Without the ECU, the car's engine cannot operate normally. ECU refers to the electronic control unit, which is a special microcomputer controller for automobiles in terms of purpose. It is composed of a microprocessor, memory, input and output interfaces, analog-to-digital converters, and large-scale integrated circuits such as shaping and driving. Take the 2016 1.8T automatic premium model of Citroen C5 as an example. Its length, width and height are 4825mm, 1860mm, and 1480mm respectively, the wheelbase is 2815mm, and the fuel tank volume is 70 liters.