Changed coil pack, now throwing cat code

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I just changed the coil pack and MAF sensor on my 2003 Jetta (230k miles) and literally the day after I"m getting a P0420 error code, for the catalytic converter. It was misfiring when starting in damp conditions and rough idling, but I didn't let it go on for long and it only misfired a handful of times.

What's strange to me is that it didn't throw a code until I fixed the issue...does anyone know if this is merely coincidence or if fixing it could have tripped up the o2 sensor? (or something else I can't think of)

That said, I don't notice any symptoms that the cat is acting up. I deleted the code but it came back after a few days unfortunately.

If I removed the source of the misfires, will the cat continue to decline or will it just stay mildly impaired/clogged?
 
What engine do you have?

I'm not sure about VW, but in many cases the catalyst monitor usually doesn't even run until all the other monitors are complete AND there's no CEL code. So that's why you wouldn't get the P0420 code until after fixing other issues.

Before you replaced the coils, when it was misfiring, was the CEL blinking? Because this is VERY serious and indicates something that can damage the catalyst. You had raw gas going in the converter.

But if you have the P0420, usually the converter is already declined.

Do you have a VAG-COM?
 
Oftentimes it won't do emissions checks until there are no active codes. It doesn't take much misfiring to kill a cat especially on an older vehicle with a lot of miles.
 
Is it a 2.slow? My 2003 2.0 threw the same code. It can be a wide variety of things that cause it on these cars and engines. After replacing the coilpack and MAF on mine as well as both o2 sensors it turned out to be a bad cat.
 
Wow, so the check engine light from the misfires was preventing the cat light from coming on...and it only took a couple misfires to mess it up.

So I guess my question now is how long can I drive with a p0420 code? And at what efficiency percentage does the code throw? I've heard it can be as high at 95% or as low as 75%.
 
How long can you drive? I'm guessing until it fails emission inspection.
 
Originally Posted By: dogememe
It doesn't take much misfiring to kill a cat especially on an older vehicle with a lot of miles.


Bingo.
 
Originally Posted By: llmercll
Wow, so the check engine light from the misfires was preventing the cat light from coming on...and it only took a couple misfires to mess it up.

So I guess my question now is how long can I drive with a p0420 code? And at what efficiency percentage does the code throw? I've heard it can be as high at 95% or as low as 75%.


I did 50k miles with my p0420 on for a bad cat in my 03 2.0. No worries
 
Perhaps the catalytic converter got carboned up from the bad coil, or the converter is used up. If it's carboned, it should fix itself with mileage.
 
The cats on these often break up and pieces go down into the muffler once they have been overheated. Tap the cat with a mallet if it rattles you know that what happened.
 
Whippersnappers in the parts stores would sell you a $30 bottle of Cata Clean...even though they were sued and can no longer state that it will clean out a plugged up/fouled/rock hard cat.
 
Originally Posted By: NHGUY
Whippersnappers in the parts stores would sell you a $30 bottle of Cata Clean...even though they were sued and can no longer state that it will clean out a plugged up/fouled/rock hard cat.


crc guaranteed to pass (lol) is less than half the price, try that if you're gonna bother with [censored] you pour in the tank. better than that would be a good highway run on a warm day driving agressively the whole time to get the cat nice and hot. if that doesn't fix it, it's dead
 
Originally Posted By: dogememe
Originally Posted By: NHGUY
Whippersnappers in the parts stores would sell you a $30 bottle of Cata Clean...even though they were sued and can no longer state that it will clean out a plugged up/fouled/rock hard cat.


crc guaranteed to pass (lol) is less than half the price, try that if you're gonna bother with [censored] you pour in the tank. better than that would be a good highway run on a warm day driving agressively the whole time to get the cat nice and hot. if that doesn't fix it, it's dead


Rubbing alcohol is even less.
 
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