All the electronic systems in the vehicle has its own Message Identifier, (MIDs). Engine Controller, Trans, HVAC and so on. Typically generic scanner are usually very limited in what they can read, usually only the engine ECU. You can go out and buy a Snap-On reader for thousands of dollars and connect it and probably be able to select any of the MIDs. You get what you pay for in other words.
The Parameter Identifiers (PIDs) just code the different components within each of the electronic systems.
The Parameter Identifiers (PIDs) just code the different components within each of the electronic systems.