# Code P0171 Caused by Disintegrating Cat Converter?



## vwlover77 (Jan 7, 2008)

My '99 New Beetle's catalytic converter is disintegrating after 79,000 miles. The "guts" of the converter are rattling badly at certain engine speeds (I have verified that the rattle is not loose exhaust shields), and the exhaust coming out of the tailpipe smells bad. Not like rotten eggs, but like raw exhaust. This has been going on for a number of months but the exhaust smell has only shown up in the past week or so.

Two days ago, the CEL came on. I assumed this probably had something to do with unconverted exhaust reaching the oxygen sensor downstream of the cat, but the code is P0171 - System Too Lean. This does not seem to fit with the cat self-destructing, unless maybe the guts have shifted so that the downstream O2 sensor is somehow blocked from sniffing the exhaust?

I'm trying to determine if I've actually got two problems, or only one! 

Thanks from a newbie / lurker...


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## bcb5082 (Mar 27, 2011)

My jetta threw the p0171 code and after spending weeks trying to figure out the cause it turned out to be a failing MAF sensor was letting too much air into the engine. You might want to check that. HTH


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## ps2375 (Aug 13, 2003)

The second O2 sensor has nothing to do with that code.


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## Tempa1986 (Mar 31, 2011)

I have a Mk4 Golf which is giving me the fault code P0171 too.. I have been to two different garage's to have this problem fixed & both times they replaced the lambda sensor / Oxygen sensor. After driving a mile down the road, both times the emmission workshop light comes back on. 

I gather the Cat converter could be another reason why I'm getting the P0171 fault code?

If so why dont the fault code relate to the cat converter? Sorry I am a novice with cars :what:


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## ps2375 (Aug 13, 2003)

That code is generally a bad MAF. And I wouldn't let them change an O2 sensor unless there is a code for it.


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## Tempa1986 (Mar 31, 2011)

ps2375 said:


> That code is generally a bad MAF. And I wouldn't let them change an O2 sensor unless there is a code for it.


Would you suggest I change the air filter & also the Sensor?


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## ps2375 (Aug 13, 2003)

Depend upon the age/condition of the filter, and I would get the code diagnosed by a competent shop.


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## Tempa1986 (Mar 31, 2011)

Ok Thanks you ps2375


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## PBWB (Sep 12, 2004)

My post is related to the possible cat issue, not the MAF code.

My jetta had the guts blow out of it as well. There was one chunk left just big enough not to shoot out my straight through 2.5" exhaust, so I dropped the cat and broke it up and removed it. I still to this day haven't gotten an o2 sensor CEL.....but my car is "lucky and different".

Your car could also be telling you it's a lean condition because of the wrong oxygen content in the exhaust flow and subsequently dumping fuel to compensate. This happens a lot with people running test pipes and such.

But I agree, don't change an o2 sensor until you're either forced to or get a code for it.


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