Battling an intermittent P0420.

blaizemarshall

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I have a 2006 Liberty 3.7L, 187,000 miles. I have recently had both cats replaced at a muffler shop. First cat was replaced a little while ago due to rattling noise and it was found to be completely broken inside of housing. A little while later I got a p0420 and since the other cat had crapped out recently I assumed, possibly wrongly, that this one had as well. Got it replaced. P0420 came back after sensors ran. I was ignoring it for a bit and the code self cleared. After some driving it came back, then cleared again, then came back. However the second time it came back it was accompanied by a p0137, which I understood to be low voltage on Bank 1 Sensor 2. I recently changed the o2 sensor and it was pretty burnt up. I manually cleared the code and am waiting to get some driving in on it to see if it comes back and will update post if it does. If anyone has any insight on this strange intermittent-ness of these codes it would be much appreciated!


Attached is a pic of the old sensor (left) and the new one (right).
 

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Ksat

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Cat converters don't typically fail on their own. If you just replace them w/o knowing why they died then you're likely going to have to do the same thing again in short order. It is for this reason that most converter manufacturers will not warranty out their units until they've had a chance personally inspect them, especially given the stratospheric cost of the precious metals they use.

If I were to guess, the burnt up downstream O2 you showed is further evidence things are amiss in with your air/fuel mix.
 
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blaizemarshall

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I am wondering if it could be anything with the fuel injectors. I haven't had any major issues that might point to a bad injector but they most likely haven't been touched for its' life and may need some kind of cleaning/replacement?
 

Johnny O

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I am wondering if it could be anything with the fuel injectors. I haven't had any major issues that might point to a bad injector but they most likely haven't been touched for its' life and may need some kind of cleaning/replacement?
Sort of. Nothing kills a cat like a bad mix. The O2 sensors if faulty will cause the injectors to produce a rich burn, which tears up the car with excess fuel.
 

blaizemarshall

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Since I replaced that o2 sensor, I did a 7 hr road trip and have driven it around the town for a day. The light has not come back on so I am just going to wait and see for now I suppose. Injectors are something I would like to do eventually anyway so might as well start saving up.
 

blaizemarshall

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Sort of. Nothing kills a cat like a bad mix. The O2 sensors if faulty will cause the injectors to produce a rich burn, which tears up the car with excess fuel.
Since I replaced that o2 sensor, I did a 7 hr road trip and have driven it around the town for a day. The light has not come back on so I am just going to wait and see for now I suppose. Injectors are something I would like to do eventually anyway so might as well start saving up.
 

Ksat

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Get yourself a scan tool with ability to read live data/mode 6. That will help give you a better picture of how things are looking, including the injectors.
 
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