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Bad catalytic converter, P0421 - HELP!

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Old Mar 21, 2012, 09:19 PM   #1
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Bad catalytic converter, P0421 - HELP!

Okay, so I took a major gamble on buying my car. Obviously I bought my 2002 Mitsubishi Lancer O.Z. Rally used. The service engine light was on when I first looked at the car and the previous owner told me she has been driving it like that for 6 to 8 months and never got it fixed since she was told it wasn't harming the car at all since the catalytic converter isn't that bad, yet.

I took it in to get it looked at by a very trusted mechanic and he told me the situation with the car about how the computer doesn't tell him which catalytic converter it is since it has two. So it would be recommended to replace both. What I am getting at is... I'm on a budget, I don't have a grand to fork out to fix this problem. Not realizing how expensive this fix was. Does anyone have any suggestions on how I could fix this problem without breaking my wallet? Is it possible to just replace the front catalytic converter and just remove the rear one? If so... is there a way to override the sensor so my service engine light won't be on?

He checked everything else on the car and said it was well maintained, has new spark plugs, he checked all the belts and fluids and said it all checked out fine and oil changes were done regularly. So hopefully the only problem I will have with the car is the current one with the cats, probably needs new suspension as well since the car has 118k on it.

Like I said, they can't be that bad yet just for the fact that I only get that nasty smell if I step on the gas pretty hard, which I was told was one of the symptoms. On top of that I don't have that much power loss either, I was told the est time 0-60 on these cars is about 9 seconds. I got about 9.8 when I timed it, speed isn't that big of a deal to me... A clean, well maintained and excellent condition car is what is a big deal to me. lol

Sorry for long post... To anyone who replies, thanks in advance!
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Old Mar 22, 2012, 08:01 AM   #2
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if it's po421 I'm pretty sure it's the second cat that's under the car, not the warm up catalyst by the engine. you could always buy a high flow catalytic converter that's obd compliant. check Roadracemotorsports.com if my memory serves me correct, it's under 200$. they also have a CEL Eliminator
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Old Apr 9, 2012, 01:42 AM   #3
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It's probably the warm up catalytic converter which is on the exhaust manifold...there is a recall for these, unfortunately the recall was only good for 8 years. You could try replacing just the rear cat with a bolt on aftermarket one, like a magnaflow...maybe it's the rear cat and I believe it would be a good time to change out the rear anyway. But I think it's probably the front cat that is throwing the code
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Old Apr 10, 2012, 03:30 PM   #4
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do you still have an engine light? go to advance auto or auto zone and have them scan your car. this is free and will give you the code and possible solutions. Right off the bat, your trusted mechanic, i would not trust him. he is either a very bad mechanic or he is ripping you off. the scanners at autozone can pretty much tell you the problem. your downstream o2 sensor monitors the pre-cat in your exhaust manifold. it has no clue the one under the car exists. it just has to fall in a range of voltage drop from upstream to downstream o2 sensor. if you have a p0420, this is your pre-cat. i would recommend buying an aftermarket header that removes the pre-cat. and put a o2 simulator in your downstream cat. this is cheapest way to go for the pre-cat. and as said by vortech vq35 this is a recall.
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Old Apr 10, 2012, 03:32 PM   #5
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if you decide you want to replace your header with a stock header. i have one i'll sell you cheap. it has 60k miles on it. i took it off when i turboed my car. i also have an aftermarket header and highflow cat if you're interested.
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Old Apr 21, 2012, 11:06 AM   #6
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If it is P0421 and you have a Lancer 02-03, it is almost always your front cat. I "fixed" it by modding the second O2 sensor, which is before the second cat, and sticking it out an inch out with a spark plug non-fouler.
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Old Nov 24, 2016, 12:57 PM   #7
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Fixing the cat....

I just pulled out my catalytic converter on the muffler ,i made of nice size hole in the honey comb. To reinstall I need two gaskets less than 20 bucks.i and clean o2 senser good to go and pass inspection. I'm not a mechanic by far ,bbut it was so simple to do. Now on the lowwer cat just change the senser. Don't need to buy the whole thing lower stream cat
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2002, bad, bad catalytic converters, catalatic, catalytic, change, converter, engine, front, lancer, light, mitshibshi, mitsubishi, problems, signs

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