CRoger

Hey guys,

I have found the error codes P0431 and P0421.
When accelerating slightly, the engine does not run smoothly either. It actually runs well, but it stutters easily, even though I reset the error codes.
But as soon as the errors come back, it becomes much more unsteady.

What is the best way to diagnose? The pre cat O2 sensors have a fluctuate measured value, as it should be.

Coils and plugs are new.
I don't think it is a combined error, but I have also the problem, that electrical components are being switched off.

Thanks for helping :-)

thorissr

these 2 codes are typically related to your catalytic converters or O2 sensors. I receive them sporadically either both or one or the other with no DTC light...just stored codes. At this moment it’s not causing drivability issues as my Cayenne runs great. There are 2 common denominator that I’ve noticed when these codes pop up, 1) Cold weather and 2) Occurs during first startup and I don’t allow the Cayenne to properly rise to a particular temperature in cold weather before driving. Theses two items are almost sure to incite these codes.

Fix? From my research I’ve connected my Durametric and as expected both my O2 sensors and Catalytic Converters “fail”. I’m not sure if it’s the up or downstream O2 sensors, but my bet will be that I need new Catalytic Converters ($$$). For the time being it’s not causing any issues, and plus I’ve had more pressing items to fix. Eventually I’ll deal with it when I have the spare cash to have new catalytic converters installed.

CRoger

Yes, you are right. But I will noch accept, that both cats are the one and only issues.
The cats are build for the lifetime of a car. In my case, the car has 135,000km. That is not really much by a modern car.
if the engine would burn oil, the cats could be damaged. Possible, it could be the AOS the Problem, but I doesn't hear a sound or wistle, or something else. On the other Hand, I don't think, that more that one O2 Sensor ist broken on the same time. It is a little confusing.

Sorry for my bad english 😉.

Rossi

These two codes are picked up by your downstream (after cat) sensors, indicating your primary cats are not running efficiently. (reading is above the limit)

Yes, cats supposed to last the lifetime of the car, but it is not that hard to destroy them. Too much unburned fuel or high oil consumption is typically the reason cats fail.

Replacing any O2 sensors will not fix these codes. Getting new cats might, but it is essential to try to determine what caused the cat deficiency, or you will destroy them again.

Is your car burning oil, do you have to add oil frequently? Failing AOS is your best bet and hope. Catalytic converters are self cleaning, if you fix the problem right away, you might be fine, before you reach the point of no return. So, yes, no rush to spring for new cats, but try to determine the cause!!!

thorissr

I like your spunk and it’s great that you won’t accept it, but just to iterate, 431/421 are codes dealing with likely your O2 sensor on Bank 1(passenger side) whether it’s pre-cat or post cat in addition to your Catalytic converter on Bank 1...again passenger side. Your next steps would be to hook up a Durametric tool to monitor/log values associated with your emissions to determine which values are fallinc our of spec. Is if the O2 sensor up/downstream? Or is it a clogged/bad catalytic converter. The AOS under the hood can easily be identified since you can easily pop the cover off to inspect the diaphragm for tears, etc.

What are your next steps since you won’t accept the possibility of potential bad cats on a 135km. If you have a Durametric tool it’ll show you right off the bat under the Engine Module whether your emissions are the root cause or at the very least, where your problem originates from. This will give you a general idea as to the root cause which will allow you to fix the issue without having to check every aspect or parts of the vehicle that can potentially be associated with these 2 codes. Believe me...it’s a timesaver and money saver!

Rossi

^^^^^ P0421 is passenger side, P0431 is related to driver side. So both side have so issues.

thorissr

I stand corrected! Thanks Rossi and you are correct....both sides.

“Error Code P0431 is defined as Warm Up Catalyst Efficiency Below Threshold (Bank 2). This code refers to a failure in the catalytic converter caused by either too much or too little fuel intake, or contamination from engine oil.”

CRoger

Thank you!
I'll make an appointment at the Porsche Centre and have a diagnostic test done.

Just a general question I asked myself last night: The AOS is more than just the gasket, isn't it? The seal is just part of the valve?

Or does the AOS consist of the complete part, as Porsche sells it. At Porsche you don't just get the gasket, you have to buy the whole part.

Rossi

Please post you diagnoses from the dealer and update if you get the problem addressed and sorted.

AOS, you can now buy just the diaphragm ($60ish)on eBay or Amazon as PORSCHE only offers the entire AOS unit ($200ish)

Rossi

Any update, is the verdict from the dealer in yet?

CRoger

@Rossi , sorry for the late answer. No, I didn't have an appointment right now. The dealer is far away and in April I have the German TÜV. I don't know the counterpart in other countries, but it is the 2 year inspection from an authority.
I will not drive often in in the next months, because of the bad weather, so I will put the appointments together.I have read your posts, and I knew you have had also this issue. As a precaution i have replaced the seal of the oil separator, Afterwards I have recognized, that the long term fuel trim has decreased a little and moved between 3-4%. The other bank is at 2%. Although I am not 100% sure, because I don't have much reference values from the past...

Rossi

^^^ thank you for posting the update. Yes, still hoping to hear for some conclusions.

CRoger

I have some questions @Rossi
Do you have trouble with the battery or charging the car with the attenuator? Does it starts fine and the starter is always turning ?
What shows your voltmeter in the display, when you are driving?

thorissr

@Rossi...yes it burnt oil @ approximately 1/2QT every 1.5 - 2K miles (198K on the dial). Since my last post on this thread I've replaced both intake valve covers with new ones, new intake valve cover gaskets installed, intake manifold gaskets replaced along with a new AOS diaphragm whch was installed when the driver side intake valve cover was replaced. I no longer experience smoke when I drive spirited, and haven't had to add oil since these repairs have been done.

At one point I thought my P0431 issue was resolved when for the first time all emission tests yielded "pass" for all categories. However, about 3 days afterwards the dreaded P0431 came back again along with a DTC light. Once I clear it I can go days without it ever cropping up, and out of the blue it'll come back with no rhyme or reason that I can nail down. Is there a possibility that my Cats have been clogged up from the burning of oil through the cats and they just need a good cleaning? BTW....I haven't received the P0421 code since my recent repairs.

Thanks

Dilberto

P0421 and P0431 warmup catalyst codes can be permanently squelched with these oxygen sensor bungs: