Lincoln/Mercury Repair: 2000 mercury check engine lights, 2000 mercury cougar, catalytic convertor

Question
hi. i have a 2000 mercury cougar and from time to time check engine light comes on.after adding c-foam or fuel system cleaner and scanning the system the light goes off for2-3 weeks and then comes back on..everytime i took the car to the dealer the guy scanned it and the light went off and the trouble code was 420 something about catalytic convertor.should i change the catalytic convertor?  

Answer
Hi Rita, Please don't answer the first one! I see you got it here.

Just FYI, the easiest, best way to clean the fuel system is Shell Premium. Run a few tanks of it and this will clean the entire system. I mention Shell because my car runs so good on it. I want to ask you why you decided the fuel system needed to be cleaned? Can you give me the symptoms leading up to adding the additive or was it just routine maintainance? The codes P0420 and P0430 indicate a substance in the fuel that is breaking down the catalyst in the catalytic converter. Engine operation above acceptible ranges. I am assuming it's the additive, But it also states that it could be a a clogged 02 sensor which is a lot less expensive. I am looking at the diagnostic chart for these DTC's and there is a number of tests that need to be done before just throwing a cat in there. I suggest taking it to a GOOD general repair facility and have them diagnose it properly so you don't spend unnecessary money on something that might not fix it. Hope this is what you were looking for. If not, resubmit and we'll try again!