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500pro

Cayenne S EOBD Codes P0431 and P0421

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Hi all, I am new to the forum, I have an 05 Cayenne S and last week the check engine light came on, I had it checked and the 2 codes that came up were P0431 and P0421, Catalytic converter slow to warm bank 1 and bank 2 respectfully. The car ran perfectly well, we therefore had the codes cleared and decided to leave it to see if the lights came back. 1 week later and the check engine light has reappeared with the same codes. Now generally when these codes appear they suggest either worn or faulty catalytic converters or exhaust leak or lambda sensors. However I find this hard to believe as the car has only done 34kmiles, also I wouldn't expect both cats to be in recording the same faults. Has anyone any ideas or come across this before? I have also read that some manufacturers have similar faults and its down to the monitoring tolerance being too stringent and they have changed there values to cure the fault via flash coding.

I will welcome any suggestions. Thanks in advance.

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P0421 Catalytic conversion, bank 1 – above limit value

Possible cause of fault

- Oxygen sensors in front of and behind catalytic converter are interchanged

- Catalytic converter faulty

P0431 Catalytic conversion, bank 2 – above limit value

Possible cause of fault

- Oxygen sensors in front of and behind catalytic converter are interchanged

- Catalytic converter faulty

You will need a tool that read the O2 sensor voltages.

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i had the same troubles with my 05 Cayenne Turbo , that sometimes it show the same errors by durametric diagnostic. Error was usually cleared by self when i´ve purchase 100 octane racing fuel by Shell after few km, so i think that its a low quality fuel what makes this troubles. I realise so its hard sometimes reach 98 or higher octanes in USA.

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I have a 2008 Cayenne S and was told to do a cat bypass, how do I know which cats are the problem?

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I have a 2008 Cayenne S and was told to do a cat bypass, how do I know which cats are the problem?

 

The code will tell you which one (e.g., which bank).

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On 11/24/2008 at 4:37 PM, Loren said:

P0421 Catalytic conversion, bank 1 – above limit value

Possible cause of fault

- Oxygen sensors in front of and behind catalytic converter are interchanged

- Catalytic converter faulty

P0431 Catalytic conversion, bank 2 – above limit value

Possible cause of fault

- Oxygen sensors in front of and behind catalytic converter are interchanged

- Catalytic converter faulty

You will need a tool that read the O2 sensor voltages.

 
Just got my GTS back from the major repair, front of the car was removed, so was the front subframe as we did front main seal, upper oil pan reseal.

One week later, about 400 miles later .... just popped up CELs P0421 & P0431.
 
In my situation of both codes popping up after major repair, it is very probable that front (upstream) and rear (downstream) oxygen sensors were interchanged right? 

 
 
 

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1 hour ago, rossi said:
 
Just got my GTS back from the major repair, front of the car was removed, so was the front subframe as we did front main seal, upper oil pan reseal.

One week later, about 400 miles later .... just popped up CELs P0421 & P0431.
 
In my situation of both codes popping up after major repair, it is very probable that front (upstream) and rear (downstream) oxygen sensors were interchanged right? 

 
 
 

 

Take it back to whoever did the repairs and tell them to make it right.

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I just spoke with the repair shop, They did not touch the O2 sensors, I might not be on the right track I guess.

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3 hours ago, rossi said:

I just spoke with the repair shop, They did not touch the O2 sensors, I might not be on the right track I guess.

The codes indicate that the warmup cats are operating below the efficiency threshold.

spacer.png

spacer.png

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Thank you JFP, what do you think is causing both code to pop up like this?

I doubt both cats are just about to go.

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38 minutes ago, rossi said:

Thank you JFP, what do you think is causing both code to pop up like this?

I doubt both cats are just about to go.

 

You need a scan tool that reads the O2 sensor voltages in real time, and preferably graphs the values.  One sensor on each side should by cycling, while the other draws a straight voltage line.  If both are cycling, one of the sensors is out.  My concern would be that someone just worked on the car and may of crated a wiring issue that is screwing up one sensor on each side, causing the issue.  This is where there is no substitute for the correct diagnostic equipment.

 

I would start by using the above chart to determine that you really have the correct sensor in the correct locations; otherwise you will be chasing your tail trying to sort this out......

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Nothing really.  You need to see a trace of the voltage movement over time for both sensors on the same side at the same time.  Should look like this:

 

spacer.png

 

If they follow each other like this, you have a bad sensor:

 

spacer.png

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Posted (edited)

I hope I am doing this right, I definitely have fluctuation of the rear ones. This is at idle. Bank 2 looks all screwed up range wise ? The rear ones (red) show way more action. Don’t they look interchanged? 

A8FC9593-1D32-4674-8367-41B5686779A6.jpeg

892A320D-E1DF-41FC-B36D-2F29744841C2.jpeg

Edited by rossi

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Just realized the scanner should be in higher RPMs then just idle, I will re-test.

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8 hours ago, rossi said:

Just realized the scanner should be in higher RPMs then just idle, I will re-test.

 

Bank 1 seems to look much better. This is at 2100 RPM. It looks like it is running rich right? 

FDE10EEF-3DD6-4977-8C1F-9FBFA0556B84.jpeg

C4FA2750-D888-4BF7-9C31-CAF53E6ECD8C.jpeg

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This is what my catalyst monitors reported, bank two failed. Bank one barely passed.

55424A52-2A6F-4ED4-A382-A2844E04752C.jpeg

05E2CBBF-48A5-4BF2-9ADB-3E73E9F38E62.jpeg

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Refer to my first graph above; what concerns me is that you are not getting a true nearly flat line from the rear O2 sensor and a rhythmic sine wave like curve from the front sensor, yours are showing a bounce that should not be there.  You could have fouled cats.

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Posted (edited)

If you look at the black line for Pre-cat sensors, it seems to be running way too high right?

It suppose to flex between 0.1 to 1, it is pretty flat at 1. It seems to be all screwed up. 

The upstream sensors supposed to flex in values, downstream sensors should be nearly flat is my understanding, it like it is the opposite.

Edited by rossi

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If I'm not mistaken, your precat sensors are wide band so the graph is showing +/- mA fluctuating, which is normal. The postcat sensors are narrowband so they return voltage from about 0.2 to 0.9v. If the cats are good, the postcat sensors should read about 0.7v steady at idle but yours fluctuate quite a bit.

 

The lambda line should be close to 1.0 at all engine speed.

 

So in conclusion, it seems your cats are bad (barring any exhaust leaks).

 

You could use clear the codes and rum a bottle of techron or seafoam in your gas tank and see if the codes come back. Can also check the cats monitor reports to see if that makes a difference.

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6 minutes ago, Ahsai said:

If I'm not mistaken, your precat sensors are wide band so the graph is showing +/- mA fluctuating, which is normal. The postcat sensors are narrowband so they return voltage from about 0.2 to 0.9v. If the cats are good, the postcat sensors should read about 0.7v steady at idle but yours fluctuate quite a bit.

 

The lambda line should be close to 1.0 at all engine speed.

 

So in conclusion, it seems your cats are bad (barring any exhaust leaks).

 

You could use clear the codes and rum a bottle of techron or seafoam in your gas tank and see if the codes come back. Can also check the cats monitor reports to see if that makes a difference.

 

I will do that. I have one bottle of Techron and another bottle on Royal Purple MaxClean on hand. I will try that. Thank you for the input.   

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