What about the control system failure of Citroen c5 engine?

This means that the ecu is damaged. Ecu is the control computer of the engine. Ecu is called the brain of the engine. Without ecu, the engine of a car can't run normally. If the ecu is damaged, it needs to be replaced directly. There are many reasons for ecu damage, such as water ingress and high temperature.

Without ecu:

That engine is not working properly. Ecu is generally installed in the engine compartment, and there is a metal shell outside the ecu, which can help the ecu to dissipate heat and protect the ecu.