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Catalytic Converter Failure [3.8L] - P0420

71K views 32 replies 12 participants last post by  BillGrissom 
#1 · (Edited)
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!
 
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#7 ·
I cleared the code by pulling the battery and IOD fuse for a while, but the code came right back.
 
#4 ·
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.
 
#5 ·
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-à-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.
 
#6 ·
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??
 
#8 ·
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.
 
#10 ·
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)
 
#12 ·
Not entirely, I looked up the Valueline set first and put the # through DealerConnect to make sure it was still available before I posted a discontinued part.. The V-Line superseeded to the set I posted.

So other V-Line sets are still available, just not this particular set.
 
#13 ·
I don't know if they still do, but a good NAPA store used to sell their spark plug wire by the foot and you could make your own, I have done it in the past. Or you could go to a junk yard and find a totaled out front end and get a wire on a newer model to replace yours.
 
#14 ·
Okay... I mean, the plug wire is working fine as it is right now so that's not really my priority at the moment. The check engine light blaring in my face has me a bit preoccupied. haha
 
#15 ·
If you had a misfiring cylinder, it can get the converter very hot. I have seen one glowing bright orange from one plug not firing. So, it could have over time gotten it hot enough to peel off the coating off the catalyst or otherwise goof things up. If you haven't replaced the o2 sensors and the mileage is good for it, you might just replace them in the order suggested to see if it helps. I didn't have a chaser, but I used a battery terminal cleaner to clean the threads prior to reinsertion.
 
#16 ·
Dealer Didn't Help

Well, I tried something that I should've known would be futile. I called one of the service technicians at my local dealer, who has been known to give me some good advice before- just to get their take on what might be wrong. Just as I thought, he simply replied:

"You probably fried your catalytic converter. If you bring it in, we'd be happy to look at it." <-- THAT didn't do much to boost my confidence.

My gut feeling here is that this P0420 code, must be somehow related to the misfiring incident that happened- simply because of the fact that the van threw the code less than 24 hours afterward. However, since the van stopped misfiring well before the code, I don't know why the code appeared late, if that is in fact the reason it showed up at all.

The van is rapidly closing in on 130,000 miles [209,214.72 km] and as far as I know, still has the OEM oxygen sensors. Forgive the severe lack of knowledge, but I unfortunately don't know the average life-time of an O2 sensor. I'm guessing they should probably be changed soon. I'm still a little gun-shy about throwing two new O2 sensors [approx. $75] at the van when I'm not even getting any of the sixteen different O2 sensor trouble codes.

I'm really at a loss and I NEED to get this resolved. My lack of knowledge when it comes to exhaust systems doesn't even allow me to make an informed decision of whether or not it's even safe to drive the vehicle. Thus, another reason I just need to get it rectified. I'm thinking I might have to just replace the spark plug wire with a new one, and replace both of the O2 sensors as a start. But that right there is going to cost me about $100. Should I just save it, and put that cash towards shelling out for a brand-new catalytic converter replacement job?

What would you all do if it was your van?
 
#19 ·
Good to know. I mean, the van appears to be running like a top, which is why this really kills me. I just sunk a great deal of money into getting the family's PT Cruiser running right. As horrible as this is to say... would it kill the van to run like this [with a possible bad catalytic converter] for a little bit while I try save to afford this est. $500 catalytic converter replacement? [I don't need the lectures about how it would be bad for the environment, but one has to do what they have to do sadly...]
 
#18 ·
I'd probably replace the O2 sensors. My Dakota has needed both of them already (176,000 miles), and one of them threw a code for me (the rear one). The front one wasn't throwing a code, but overall engine performance just didn't seem quite "on", and I replaced it and all became well.

My hunch is that the mis-fire baked the converter. Unless Colorado is anything like California, you can get a very affordable universal aftermarket converter installed for a few hundred bucks (including part and labor). I had one put on my Dakota about a year ago, for $200 even at a local exhaust shop. The old one sounded like marbles in a tin can.
 
#20 ·
You don't really have to fix it unless the engine starts bogging down real bad. And it shouldn't cost you more than a couple of hundred dollars to get it replaced by a good exhaust shop. The part itself is only about $75-90 online (such as through Rock Auto, Summit Racing, etc).
 
#21 ·
The problem is, I have to find a third-party shop that I trust. Sadly the only shop around here that has gained my trust is the dealer. Who is most likely going to want $500 at least to do the repair. Most of the other shops around here are gas station repair shops. They always seem a bit shady to me...
 
#22 ·
if I am not mistaking you have complained in the past about poor performance on this van compared to your 96 3.3, this may be why and just now it is throwing a code, spark is one thing, cat, it is abit of a job especialy to get those bolts undone, I had to torch mine, I would never spend $500 on a cat job, though the bolts and gasket ran me $30 at the dealer, you can get them fairly cheap, and have smb weld it in, like jason said $200 should be good, as for the o2, I have been buying them on ebay for about $30, bought several of them from one of those vendors, the cheapest ones I could find, I recently got one for the van, I belive it was $26, bet if you knew that you would have done it when you did the plugs, those sensors did not look exactly the same as oem but I have used them on several cars, they have always worked for me, pluged, and threaded right, rumor has it o2 sensors lifespan is less than 100k, your owners manual might have something on that, and just because they don't throw a code does not mean they are still good, they could read wrong but within specs, if it were my van I vould be more concerned about finding some good deals and do it all, including the plugs and wires, I'd do them again, might be able to get it all done for $500 if you shop right and do as much yourself, like I said, you have complained about the performace of this van, I'm sure it has a litle bit to do with all this, changing the cat when the o2 are still bad may plug the new one quick, and if it has been running rich or lean all this time your plugs may show it. GOOD LUCK.
 
#26 ·
and if it has been running rich or lean all this time your plugs may show it. GOOD LUCK.
What would the plugs look like if it was running rich or lean?
 
#25 ·
Normally, I would go to the shop that did my muffler- but currently I'm not home in Colorado- I'm helping my family move- so I am on the other side of the country in CT. Where the only shop I trust around here would be the local dealer. Alas it looks like I fried the blasted converter.

It was only misfiring for two days! And I wasn't driving all that much those two days either. Sigh.
 
#29 ·
It was only misfiring for two days! And I wasn't driving all that much those two days either. Sigh.
It may have been failing for much longer than that, but without you realizing it. Sometimes misses are hard to feel, and will go not noticed by the computer.
 
#27 ·
Chrysler 1924 I'd find a muffler shop close to you. Go eat at a local resturant, make small talk with some of the guys and ask them about an exhaust shop they would trust. OR go to the dealer and ask them for any good aftermarket exhaust shops. I replaced the cat and both O2 sensors on the 97 at around 150K mi. It did have the downstream O2 sensor code (can't remember which one) and I didn't see the point of putting a new sensor in an old cat. That took care of my issue.
 
#31 ·
The ECM's and its sensors can work in strange and mysterious ways.
A while ago my dad decided that we needed a surprise visit to Mexico. Being that I'm afraid of flying and flying also takes a huge bite out of wallets, we drove our 2003 Dodge Ram from L.A. for 1407 miles to my grandmas.
The trip south was trouble free, but during the stay the MIL came on. It was there that I realized that I forgot to pack my OBDII code reader (I usually bring it with me on extended trips in case of such occurrences); luckily I was able to get the code from the odometer by turning the ignition key three times between the on and off positions.
P0421 Warm up catalyst efficiency below threshold (Bank 1). Basically, out of the four O2 sensors in our truck, the two in the left exhaust pipe were detecting that there was not that much catalyst action between the upstream and downstream O2 sensors.
I then deduced that either: 1. one of the sensors was faulty or 2. the fuel (only PEMEX in Mexico) was not sitting well with the truck. It never occurred to me that the catalyst was at fault and that never proved to be the case.
At first I disconnected the battery to see if that would help, but all I managed to do was upset the engine since anytime the ECM is reset the engine can't idle well and it continuously stalls. The MIL light came on after the 10th start up.
So there was something wrong with the truck. What with spare parts being hard to find in such a short notice, I went with the idea that the fuel was at fault. So I changed the oil and then added a Chevron fuel injector cleaner at the next fill up. Reset the ECM and waited; the MIL didn't come on again for the rest of the trip.
After we returned however, the MIL came on again. This time though, I got code P0058, oxygen sensor heater circuit high voltage (Bank 2, Sensor 2). Now the the downstream O2 sensor on the right exhaust pipe was at fault. More straight forward time since it could only be one of two problems either the sensor was bad or the wiring was shorting somewhere. Turns out the sensor was in bad conditions, even though the truck still had the original sensors at 60,000 miles.
One oxygen sensor, fuel treatment, and reset later and all is fine. Still no sign of further problems.
I don't even know if this will help with your problem, it's just that since the problems are slightly connected it might help prevent the expense of changing the catalytic converter. Also if you say that the engine miss started only recently then it seems unlikely that a few miles of driving with unburnt fuel flowing out the exhaust will cause such damage to the catalytic converter. Try the sensors first, way much cheaper to replace and they might also set off the catalytic converter code.
 
#33 ·
An old thread, so past posters may be gone, but a common problem. I got the P0420 code in our 2002 3.8L T&C. After research, I changed the cat converter and fixed it. Today, you can buy an ELM327 adapter for the OBDII port for <$10 (ebay) and run a fee app (ex. TorqueLite) on your smartphone via Bluetooth. Plotting the upstream & downstream O2 signals proved the cat was the problem. Mine is a CA/NY engine, so pricier. I recall ~$280 on rockauto. Changed it myself. Prior to that, I tried cleaning it w/ lacquer thinner per ebay and viewing the catalyst w/ an endoscope (thru upstream O2 sensor port).
 
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