Definitely not always. It used to be that a mechanic or a skilled owner could tune, modify, repair or replace absolutely anything in your car. That was basically since the invention of the car, up to somewhere in the 2000s. And even then, various hackers and pirates made sure almost anyone could get their hands on the software. In fact, many mechanics these days use 3rd party software because the manufacturer refuses to sell them their version or even that version doesn't have all the features.