Thread: P0421 Code
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Old 08-30-2010, 01:52 PM   #13
snicknc
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Join Date: Aug 2010
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2002 VUE 3.0L
Default Re: P0421 Code

I called a muffler shop for a quote on a new cat (versus just welding one on myself), as I'm running out of time with this car, and the guy there said that the catalytic converter company he sources from stated that P0421 is an indication of coolant hitting the cat 90% of the time.

He went so far as to recommend NOT replacing the cat until I figured out what's causing the code. I guess the idea is that the cat is not actually failing, but is simply having its efficiency hindered. I know absolutely zero about the inner workings of catalytic converters, so does this sound about right?

I am not relishing the thought of head gasket change, but I'm not blowing any smoke at all, overheating, or seeing my coolant levels drop, so I'm wondering if it's actually the intake manifold gasket leaking (if coolant contamination is the culprit at all). I'll go ahead and pull the intake over the next couple of days, I suppose, and see what I can find. I just finished swapping the head gaskets on my brother's Dakota-- geez. Talk about the month of vehicle maintenance.

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