What is an ECM Scanner or OBD-II?

Fot today's day and age mostly eveyone has new engines that have what is known as ECM or ECU ( Electronic Control Module or Electronic Control Unit ) and it is the brain of the engine, it has parameters for each of the systems that make an engine Work and depending on those parameters if they are exposed to an irregular value which would be done by the sensor component that is monitoring a dedicated area of the system which could be for example, the fuel system has the pump and some sensor on the fuel filter, after that it goes usually to a fuel rail where it also has a sensor and then at the injectors which have built in sensors for monitoring and programming the amount of spray going to the cylinder. But the engine has more components and systems so all of them are tied to the ecm which decides if your engine is optimal for all the regulations now a days, if it has something off it will reduce your performance, that is where an ECM Scanner is needed and optimal, for the codes that come up or some live performance details to determine what might be wrong with the enigne so the mechanic can do what is needed to bring back your engine to optimal performance.