Actualy I was doing some more reading today, none of the early systems had anything that will log codes or dectect problems as such, so you are right there.
But faults can still be detected via the computers on these early models, the fault reading/checking function is part of the service computer, when it gets hooked up to the computer on your car it fully checks out the system and can tell you what is wrong with the car, it tests every part of the system.

It's interesting because later computers must basicly have part of the service computers functions built into them, meaning all the later service computers needed later on was a reader of some sort.

Of course on teh down side this means I have to go in somewhere now to find out what is wrong with my system!
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Veronica, my 85 760Ti