Sorry dude, your in the same boat and up the same creek as me, early units have no "check engine" light on the dash, and seem to have no in built check feature either.

It's a big pain because there can be a dozen things wrong with the system but unless you have the equipment you just can't find out what is wrong.

It was not really an issue when they were new, at your regular service they would just hook it up and check it as part of the service, but these days it just makes it rather user unfriendly if you want to do all the servicing yourself.

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Veronica, my 85 760Ti