95 Century diagnostic tool ?

What is the special diagnostic tool and about how much is it? I know the jumper tool wont work. I have some 3 wire setup.

I need to diagnose my service engine soon light. It has been constant until I put high octane gas in it. But I put some of the mid grade gas it in and now the light has come back on. Its a yellow light. I also have a ticking noise coming from the motor but goes away 60 sec later. Any pro help would be greatly apprecated.