Pretty much what Raymond said.

I know it's sort of verboten to talk of such things here, but God bless those various software leakers and "crackers" that release manufacturer/dealer specific software tools.

My advice would be to just get a cheapo OBD2 reader first and foremost. That will cover about 75-80% of all codes that pop up on all of your cars. A friend of mine gifted me one of these when I helped him with his car. All it is is a simple OBD2 plug, a wire, and a small unit with 2 buttons on it (read / clear). No batteries or fancy anything.

If you want to go further, do some research on your specific vehicle make and models as to the software availability and the cabling needed. Then, go out and buy a cheapo laptop that can connect over the proprietary cabling for your cars. If you have an old laptop lying around, this is a good task to put it to work for.

This might require some troubleshooting and hackery on your part to make the software work. Find a millennial or "youngin" to help you walk through how to do it. Just make sure to keep it off of the internet.

If you want something that just works, you might want to go spend money on the more expensive off the shelf stuff. But even then, those might not do all of what you need to do.

T'is the future of automobilia sadly.

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-Typos courtesy of my mobile phone.