I just wanted to post this information for anyone facing the same issue I have faced over and over for several years with my 2000 S-Type 3.0L 6-Cylinder. I had replaced many parts including ignition coils, O2 sensors, and Vacuum lines and elbows some of which presented other OBD codes along the way, but either P0420 or P0430 OR Both were present all along the way. I refused to spend $500-800 for new Catalytic converters + labor when my car ran fine at all speeds and rpms otherwise. Yet, it would have failed the State Inspection (SI) Emissions test last year and this year if not for one thing I tried that, at least temporarily got me thru the SI. I know some techs are religious about spending the $$$$$$$$$$ to fix what is wrong, simply because the car was designed to operate within certain tolerences, but let's face it they are simply that - TOLERENCES. Just because you are 1-100th over or under the STATE IMPOSED tolerences, your car will FAIL the SI Emissions test, even if there are no other adverse indications of performance. BTW - I used so many $ signs because it can go on and on and on in cost when you subscribe to the "tech" philosophy. For those of you who are thinking "if you can't afford to fix it, you shouldn't drive a Jaguar," let's also face the fact that there is nothing luxurious about an S-Type. IT IS A SUPED-UP FORD TAURUS. Anyway, the one thing I did differently last year and again this year that got me thru the SI was add a bottle of RXP fuel additive $6.99 to a half tank of fuel and clearing the codes prior to the inspection. (You can purchase a pocket scanner at any auto supply store for around $49 on sale, and check to see when the OBDII monitors are in READY mode so that the SI can be done. TX requires 6 out of 8 monitors to be in READY mode to pass.) I can't swear by it yet, but I think it is more than just a coincidence that it has eliminated at least for now the P0420 and P0430 codes that were rampant before as the Catalyst monitor entered the REady mode. As of yet, the codes have not returned, and I admit that they might, but I have again avoided the unnecessary expense of replacing the CATS for now. And Hey- the state got their money for the rediculous emissions test (if the SI was really about pollution control then San Antonio with all their low-income citizens driving rigged up used cars would have the same standards as Dallas, Tarrant, and Denton counties where I live), I got my SI for another year, and my car still runs fine just like last year. The only loser here is the Jaguar Tech and the engineers who designed the system to force you to buy more parts more frequently so they can get more of your money. Yes - I am a bit of a cynic...but very very pragmatic.
You could fix the fault, but hey you're happy with your own way.
You really don't know much about the S-Type if you think it's in any sense a Taurus.
STR 2004. Acronyms: http://www.jaguarforums.com/forum/s-...-jaguar-78910/
If you would like the most accurate assistance, it is very helpful to place your vehicle information into your signature line, just look in your member control panel to set it up. Info like year, model, engine size, and other details like mileage can only aid in receiving more replies with the correct information. (thanks, h20boy!)