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1998 Mazda Millenia check engine light

I have a 98 Mazda Millenia with a CEL that I’ve battled with for about two years. I’ve had two O2 sensors replaced and other issues I can’t remember, but after each fix the light comes back on within a few weeks or so. I read one post that said the Millenia has issues with carbon build-up on the exhaust valves that can cause the CEL to come on. I use premium gas in the car, could that have an effect? (is premium gas necessary) Thanks for any thoughts.

Is premium gas necessary? I don’t know the answer to that question, but I can guarantee that it is answered in the Owner’s Manual. If you don’t have a manual, you need to get one–for many reasons. E-bay is a good source for low-priced Owner’s Manuals.

But, to return to the matter of your car, I think that a lot has to do with whether this is the “S” model, which has a supercharged Miller Cycle engine. If yours is one of these, you really need to take it to a Mazda dealership, as most mechanics have never worked on a Miller Cycle engine and would likely have no clue regarding how it differs from a typical 4-cycle gasoline engine.

If your Millenia is not an “S” model, any competent mechanic should be able to diagnose the problem. Perhaps you just need a better mechanic.

Maybe you could give is a hint from the girl in the class; The CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.