When OBDI came out, the rage was "everything will be standardized across the board". My big old butt. When OBDII came out the rage was "everything will be standardized across the board". We all just laughed. Every automaker has "their own version" of what was supposed to be "standardized" and you need 20K worth of diagnostic tools and adapters and connectors to read everything. Don't give me the "computer cars are easier" bullshit. Keep it to yourself. I was THERE when it all started and all it did was make money for rich politicians and that's all it still does. That and it makes DAMN SURE there'll be clapped out computer cars sitting in a lot of back yards, because either no one can diagnose what's wrong, OR the owners cannot afford to have them fixed.
This is basically the rage against things you are unwilling to understand mentality. The cars as they get newer practically scream whats wrong at you. Most failures are pattern failures so once the cars get old every single issue has been seen before and it's just connect the dots. In an extreme case you might have to read a wiring diagram or use an ocilliscope.
OBD1 cars have different connectors and whatnot but the codes are only somewhat useful and there's extremely limited live data, but then again most of them you can read the codes with a paper clip and use google. The things that fail most on these cars are fuel pumps, oxygen sensors, and ignition parts. Most are basically old engines with EFI retrofits. Pretty simple systems regardless.
OBD2, any year 1996-2025 you can read the codes out of the PCM with the same tool, I use a bluetooth dongle with my phone and can read live data. There is some special stuff for communicating with other modules and self tests but the universal scanners that are more expensive can do all that, never needed one. And these are maybe like $850 scanners right now.
My Dad has a 94 Cutlass Supreme Convertible that is as old as my Duster was when I got it in 2000, this thing has everything original except the timing belt, fuel pump, wires, hoses, ignition module, radiator, exhaust you name it, Starts reliabliy every time, runs perfect. Hasn't had an issue for 19 years. The Duster and most of our Mopars had at least a few carb rebuilds, a fuel pump, how many sets of points, wires, plugs, etc over 30 years? Even cars that get driven every year but rarely how long do you go between taking the carb apart? 10-12 years if you're lucky, probably less with ethanol fuel now. Did my EFI conversion 9 years ago and haven't done anything but play with the tune on the laptop.
My friend literally daily drives a 1996 K2500 pickup that's around 250k miles, original engine, all working flawlessly without a check engine light. Don't have to wrench on it all the time.
Carb problems and crappy wiring and the older engines and transmissions wearing out, plus carburators that are not set that great not being good in winter killed a whole ton of carb cars. Living in the north all my life, not that many people daily drove cars with carbs by the mid-late 90s. You almost never see anyone DD'ing a carbed 70s or 80s car though I still regularly see late 80s and early 90s EFI stuff. This area you see 88-98 Chevy full size trucks constantly.
EFI improved the lifespan, fuel economy, and reliability of the cars. They got a little crazy on some of the other electronics but the things that make it run were made better.
The additional issue with older cars is the replacement part quality is right in the absolute crapper now.
I remember buying a car that "nobody" could fix and all you had to do was start it and uplug the #3 fuel injector that was stuck wide open and you knew that was the problem because the engine ran better, bought a new injector and it ran like new. Its like anything, its a little different so you have to understand how it works first.
