ECU is a stand alone unit as in "unit" term gives the message itself. It can communicate with several units by itself. It was the most populer one when the engines were kind of in-between mechanical and electromechanical. In those times, there was few to consider in terms of engine working algorithm.

In terms of vehicles and ECU is an electronic control unit, which can be found in various systems such as ABS, ECM and BCM. These will be coded and set up in a way which they control a particular system on the car for example ECM = Engine control module its job is to control the engine, BCM = Body Control Module this controls things such as seat recognition and various other sub systems. Vehicles nowadays are designed where multiple ECUs can read the same data and over lap but wont necessarily control those components, like engine module needs data from the brake module but wont directly control those components it needs data from. So ECUs are everywhere in a vehicles today and with the more sensors we have the more ECUs we need.

All sofisticated internal combustion engine families have ECM in today's world. Because they are also monitoring and controlling aftertreatment systems, including dosing unit, some control modules. Dedication to the engine itself is kind of expensive solution, ECM covers everything in terms of emission.

ECMs are covering much wider area in EE architecture than ECUs. But that does not mean that they cannot work together. If there is a such design in engine, they can surely work tıgether to maintain the engine working process. In today's world, with the new generation of internal combustion engines, there is few examples of them working together. Because the technology and expectations are so high that manufacturers intend to solve everything in one unit that controls everything, solves everthing and operates everything.

They can control engine parameters in events of sudden needs or throguh programmable features, such as torque, maximum speed and safety of the vehicle.

The way the ECM controls the engine for vehicle performance is via a set of parameters that is ‘coded’ to the ECM from factory normally known as a factory flash, these keep the engine and sub systems at optimum range and performance within those parameters set, for example the engine coolant it will be coded that normal operating range can be between 80-100 degrees Celsius anything over will be considered overheating and anything less warm up stage for restricted power and protection of the engine, but there can be tolerances to these parameters, take the 80-100 degrees celsius parameter it can be coded to allow a 5 degree tolerance due to environmental conditions that cause it to be out of the range like temp or idling

In ECU stand alone case with less technological engines, there is not much parameter to monitor and control. But the Euro emission zone increases day by day, there are other things to control including aftertreatment systems, sensors, switches and other CAN communicating components

Literature research msut be handy but most valuable and detailed information can be access through engine manufacturers, they are producing these and they are the most important parts in an internal combustion engine.

Best way if you’re a vehicle technician is the manufacturers factory training you learn how they work how to diagnose and read the required data they use and see and how to effectively tell if an ECU is operating as it should or not.

Learning about ECM, considering all manufacturers are shifted to this, is about studying both theoric and practice. Hands on practice is the most important part of it.