Only partially. I used to work for a third party diagnosis tool company, and we had direct access to information from all companies, which they had to legally give us. I still reverse engineered a lot of things because when I.didn't understand the spec seeing what their tool did made it make sense.

I haf this discussion with mechnic friend a while ago, obviously not not a 40 year old car so. Our true second car is now, I have to guess, 15 years old. Diagnostics are no problem, computers with the correct software are around 400 bucks. Cheap enough for either an enyhisiast or free mechanic. The main car is 4 now, diagnostics equipment is only OEM, and goes for 5 figures. Go figure, but it explains why diagnostic jours can be so expensive.