Catalytic Converter Failure [3.8L] - P0420



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Thread: Catalytic Converter Failure [3.8L] - P0420

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    Exclamation Catalytic Converter Failure [3.8L] - P0420

    So a couple days ago I noticed that my van was running a bit off. No stalling or anything like that, but the engine wasn't running quite as smoothly as normal. Every so often there would be a momentary hiccup where the RPMs sounded like they drop for a fraction of a second and then return. Like:

    rrrrrrrrrrrrrrrrrrrr|!|rrrrrrrrrrrrrrrrr|!|rrrr|!| rrrrrrrrrrrrrrr|!|rrrrrrrrrr

    It turns out I had a spark plug wire that had the metal clip which connects to the plug, making intermittent contact with the actual plug wire it's supposed to be crimped onto inside the rubber boot. Apparently when I did my plugs and wires last year, I must've confused one of the wires and I ended up putting one of the original/OEM wires BACK into the van and must've thrown out the new one, without even realizing it. Because the plug that failed was clearly not one of the new Bosch ones that all five of the other ones have.

    So, I was able to fix the spark plug wire because you can't buy just one spark plug wire- you have to buy an entire set which I don't want to do. I repaired it and attached the metal clip. When I put the repaired plug wire back on the van, it immediately stopped running roughly and ran smooth as ever. Problem solved [I thought], at least until I can stomach purchasing a whole other set of wires for just this one.

    Well... that was yesterday. I drove the van around all this morning and this afternoon fine, absolutely no issue at all. Then a few hours ago, my check-engine light turned on with a P0420 code. According to my research:

    -----------------------------------------------------------------------------------

    P0420 = Catalyst efficiency low-bank 1

    Explanation: The oxygen sensors monitor the catalytic converter's ability to store oxygen.

    Probable Cause:
    1. Catalytic converter defective (failure possibly due to # 2,3, or 4)
    2. Engine misfire or running condition
    3. Large vacuum leak
    4. Engine oil leakage into exhaust-valve guide, seals, piston rings
    -----------------------------------------------------------------------------------

    Here's what I don't understand. The CEL never once came on when the van had the misfire problem due to that faulty wire. The van has been fixed, and it's not misfiring anymore... then almost a day after it's repaired **NOW** the CEL comes on saying that the misfire is possibly what's causing this.

    I highly doubt it is related to #4 [Engine Oil Leakage] because of the fact that the van does not appear to be burning oil, and nothing indicating such a leak is coming out of the tail pipe.

    Concerning #3, I feel like if the van had a "large vacuum leak" it would be experience a host of other problems, the least of which would be stalling whenever the van comes to a stop. Which, it's not doing either.

    So that brings me back to #1, Engine Misfire or Running Condition. But again, the van isn't misfiring anymore. So, just to verify it isn't a code left over from if it came on and I didn't notice while it was misfiring, I cleared the codes by removing the battery and IOD fuse. When I put them back in and started the van, the CEL wasn't lit. However after it ran for about 20 seconds, the CEL came back on with the same code.

    My only other thought would be something is going wrong with the O2 sensors, since they are the ones obviously sensing this problem and reporting it. But, my research also indicates that there are at least 16 seperate diagnostic trouble codes devoted soley to O2-sensor problems, none of which I'm getting. Which leads to me think the O2 sensors aren't an issue.

    Of course, the catalytic converter could have just up and died. But... the van doesn't have that many miles on it in the scheme of things and it's not an ancient vehicle [2000].

    So now, I'm confused. Help!
    Last edited by Chrysler1924; 09-09-2009 at 08:34 PM.
    1996 Chrysler Town & Country LX [My lovable Daily-Driver]
    2000 Chrysler Town & Country Limited [Yes, it's still around!]
    2000 Chrysler 300M [New kid on the block...]

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  3. #2
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    This converter efficiency is monitored by comparing the waveforms from two oxygen sensors.
    Try changing the front sensor first, much cheaper than the converter.
    It worked for me when I had the same code on my Subaru.

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    Try clearing the code and see if it resets.

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    The misfire may have been allowing unburned fuel into the converter, heating it up past its designed temperature, causing it to fail. Not really likely, but possible. It may just be a coincidence.
    '11 Toyota Camry | 2.5/6AT | Sandy Beach
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    Just a random thought...

    Could the issue with the catalytic converter be related to the low restriction muffler that Chris has on his van?

    I'm thinking that if the factory spec muffler is designed to work with a certain back-pressure vis--vis the valve overlap ground into the cam; it could be that due to the (theoretically) lower than spec back-pressure in the exhaust system, raw fuel is escaping the combustion chamber and finding its way into the catalytic converter.
    Sold: 1998 DGC Sport 3.8 (Final odo: 178,000 miles)
    Sold: 1998 Chrysler T&C LXi 3.8 (Final odo: 190,000 miles)
    Sold: 2003 DGC ES 3.8 (Final odo: 172,000 miles)
    1998 Audi A4 Quattro (5-Speed manual)
    2001 Honda Accord EX V6 (4-Speed automatic)
    2009 Mazda3 i Touring (5-Speed manual)
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    The thing is I got that muffler over a year ago, and have since put thousands of trouble-free miles on the van without any issue. I would think if it was related to the muffler, it would've come on sooner maybe??
    1996 Chrysler Town & Country LX [My lovable Daily-Driver]
    2000 Chrysler Town & Country Limited [Yes, it's still around!]
    2000 Chrysler 300M [New kid on the block...]

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    Quote Originally Posted by micondie View Post
    Try clearing the code and see if it resets.
    I cleared the code by pulling the battery and IOD fuse for a while, but the code came right back.
    1996 Chrysler Town & Country LX [My lovable Daily-Driver]
    2000 Chrysler Town & Country Limited [Yes, it's still around!]
    2000 Chrysler 300M [New kid on the block...]

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    Quote Originally Posted by Chrysler1924 View Post
    The thing is I got that muffler over a year ago, and have since put thousands of trouble-free miles on the van without any issue. I would think if it was related to the muffler, it would've come on sooner maybe??
    Funny, I kind of look at it from the other perspective where a problem wouldn't initially occur, and would only happen after enough deposits had built up inside the catalytic converter. That said, my comments were only hypothetical so don't take them too much to heart.
    Sold: 1998 DGC Sport 3.8 (Final odo: 178,000 miles)
    Sold: 1998 Chrysler T&C LXi 3.8 (Final odo: 190,000 miles)
    Sold: 2003 DGC ES 3.8 (Final odo: 172,000 miles)
    1998 Audi A4 Quattro (5-Speed manual)
    2001 Honda Accord EX V6 (4-Speed automatic)
    2009 Mazda3 i Touring (5-Speed manual)
    2012 VW GTI (6-Speed manual)

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    Quote Originally Posted by shipo View Post
    Funny, I kind of look at it from the other perspective where a problem wouldn't initially occur, and would only happen after enough deposits had built up inside the catalytic converter. That said, my comments were only hypothetical so don't take them too much to heart.
    Oh no, I appreciate that perspective as that is something I personally would've never thought of. Even though I have no evidence saying that it's failed... I'm wondering if I should replace both of the O2 sensors and see if that fixes it. I've never replaced the O2 sensors, meaning that they're probably OEM... and thus 9 years old.
    1996 Chrysler Town & Country LX [My lovable Daily-Driver]
    2000 Chrysler Town & Country Limited [Yes, it's still around!]
    2000 Chrysler 300M [New kid on the block...]

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    For what it's worth, The ignition wires are sold separately through the dealer,
    Here are the part numbers in the event you want cross the over in the aftermarket.

    Cyl#1 5093698AA
    Cyl#2 4686712
    Cyl#3 5093700AA
    Cyl#4 4686714
    Cyl#5 5093699AA
    Cyl#6 4686716

    As usual, the dealer wants far too much per single wire, roughly @ $22.00 each... Where as a new set runs @ $43.45 (# 4797685AB)
    10+ years as a Mopar Parts Advisor.
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