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Discussion Starter · #1 ·
I have a 98 Mercury Sable with the duratec engine, bought the car used about 2 year ago with 125k miles on it, it now has 140k. A couple of weeks ago, the check engine light came on and it scanned to be code P0430 which says: Catalyst System Efficiency below threshold (bank 2). Now the guys at autozone told me it was a bad catalytic converter, as detected by the oxygen sensor on bank 2. Could it be the O2 sensor? I know everyone always says when the O2 sensor goes out, gas mileage decreases. Well ever since the light came on, my car has gotten significantly better gas mileage, over 50 miles more per tank. Its getting almost better now in the winter than in the summer, which from my experience is usually the other way around. Is it possible that when i got my car, the O2 sensor was somewhat bad in that it called for too much fuel when it really didnt need it and now because of the engine light, the system has reverted to some default or loop setting that actually is giving me better gas mileage? A sidenote, we figured a few months ago that the car ran rich when we changed the spark plugs b/c we had to pull the intake manifold off and discovered a lot of carbon build up in there, which we cleaned out. Anyone with any experience with a similar problem? I dont want to do anything to my car that would bring the gas mileage back down, but I dont want that engine light always on either. Is there any way to keep that specific code from showing up but ignoring the problem because in my mind it isnt a problem, its as if before there was a malfunction and now in the default loop it is right. Thanks
 

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Discussion Starter · #5 ·
Thanks for the responses. Yeah it sounds like that code usually means the catalytic, but I am going to try the testing procedure on the O2 sensors first. The only thing in my case that seems unusual about the problem is the actual increase in gas mileage, why would just the catalytic going bad increase my gas mileage? Also, there are no emission tests in my area so it really doesn't matter from that standpoint to me and I dont want to spend big bucks to replace the cat. If it turns out to be the catalytic, is there any way to somehow have the computer ignore that trouble code so I can know if any other problem ever arises in the future, otherwise my check engine light always stays on. Thanks
 
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