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Discussion Starter · #1 ·
My check engine light keeps going off! I've had it reset it twice and even payed a guy who specializes in a variety of foreign cars to look at my car the second time to see what was wrong. He reset the check engine light after cleaning my plugs and checking timing, compression, etc. He says it runs great and can't find a thing wrong. He told me to run premium fuel and techron injector cleaner. My gas mileage went up after all of that and that's great, but the light came on again after about a week and a half! The only thing I can think of now is to change the plugs/wires. The code the cel is throwing is something about "warm up catalyst." I've thought about taking it to a mitsubishi dealer to look at, but I think they'll charge me a lot so if you guys have any suggestions that could save me some money I would greatly appreciate it. Thanks!

Jon
 

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well. ok. firstly, your lancer has two cats. one of them right after the exhaust manifold, and one right after the flex pipe. the first one is placed right after the manifold so that the hot exhaust gasses heat it right up so the cat starts working asap. a cat only works when brought to a specific temperature (like an O2 sensor or smtg), so in order for it to work right, it has to be heated up so that the filter of iridium and whatever else is in that grateing that generates the reaction to clean your exhaust actually works. apparently, some sensor in your cat is not working that is telling the computer that the cat is actually warmed up. idk why or how, or where it is, but that is my theory. hope i helped,

-S.E.
 

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Thanks for the reply. Also I forgot, I have another problem. How can you tell if you have a busted motor mount? I just put a front upper strut brace under the hood and when I put the car in the reverse (auto trans) the throttle body rattles fairly badly against my strut. Sometimes in drive it also rattles too, or when I go up or down a hill. I had my friend sit in the car and change from park to reverse and then to drive while I watched the engine and there is noticable movement in the gear changes. Thanks.

Jon
 

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If the code you get from the CEL is P0421, see the attached PDF's.
The four causes for this code could be:

Catalytic converter deteriorated.
Heated oxygen sensor failed.
ECM failed.
PCM failed.

There was a recall pertaining to the first catalytic converter (warm up catalyst). There was a recall to reprogram the PCM because it was incorrectly programmed and could cause the catalytic converter to deteriorate (and possible fail).

If you take it to the dealer they can tell you if the recall work was done. Depending on how many miles you have, and if they find that the cat is bad, you should get a free cat (the attached PDF about the recall has more details).

Hope that helps.
 

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ooohhh yippee, a free cat. i would be happy to get rid of mine, screw emission control. i cant wait till my new headers and flex pipe come in that will get rid of both cats.
 

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ya i have the same problem. check engine light went on at 70k throwing a code p0421.. they said it was the cat after the exhaust manifold. needs to be changed. if you buy a new one it costs an arm and leg. so i hope i have time tomorrow to check if its covered under waranty.. i already had my pcm reprogramed that had a recall as well.
 
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