Almost everything can be read by an OBD2 reader. Or there are also some homebrew options. Tractors and such start to get tricky and I am sure there are aspect

Almost everything can be read by an OBD2 reader. Or there are also some homebrew options. Tractors and such start to get tricky and I am sure there are aspects of the cars which you cannot control but from what I have seen you can get by without a reader on older cars (flashing the obd light) but on newer ones you need a decent reader. Which largely are about $100 depending on how in depth you want to go. On my VW I use the OBDeleven reader...but I believe there is a generic comparable one also. It allows you to test sensors, modules, even door switches/lights and the radio. I understand the added complexity is confusing at times but really once you have a reader it is easy enough. Code readers are actually a fairly accessible and cheap addition to your toolbox. I do agree though that the "black boxing" and DRM of hardware needs to be addressed. Especially in anything that is relied on. If you buy a machine you should get full schematics/docs/etc upon request IMHO...but that isn't really a common thing anymore.