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O2 and catalytic converter CEL


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Good evening everyone,

I've made several searches but I haven't run across one that addresses this specifically or has a resolution. Here goes:

Our new to us 2005 Cayenne V6 3.2L, 6-speed manual w/ 91,700 miles (we bought it with 82,000 miles) runs great and has given no problems for the first 6-8 months of ownership. It then gave a random CEL which I read with the Durametric to be:

P2237
Lambda control adaptation at idle, Bank 2 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and is not causing a DTC light
P2237
Lambda control adaptation at idle, Bank 2 - No signal/communication, test conditions are not-completed, fault is currently active and causing a DTC light
P2235
Lambda control adaptation at idle, Bank 1 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and is not causing a DTC light
P2235
Lambda control adaptation at idle, Bank 1 - No signal/communication, test conditions are not-completed, fault is currently active and causing a DTC light

I reset it once, switched gasoline stations (using premium 91-92 at all times) and it comes back about 4 weeks later. I change the gas cap, reset it and it comes back 3 weeks later. Searched forums and was basically looking at replacing my O2 sensors. Replaced the pre-cat sensors, cleaned the MAF and reset. CEL returned 2 weeks later. Replaced post-cat sensors and found a couple of the plastic vacuum lines had cracked next to the intake manifold. Repaired the vacuum lines, reset the CEL and it went away for almost 3 weeks. Unfortunately the CEL came back with this:

P0421
Catalyst System Efficiency Below Threshold Bank 1 - Upper limit value exceeded, test conditions are not-completed, fault is currently active and causing a DTC light
P0431
Catalyst System Efficiency Below Threshold Bank 2 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and causing a DTC light

So now I'm thinking catalytic converters but I do a bit more searching and one thread mentions that for catalytic converter to fail so early something may be causing it to fail. So now I've replaced the MAF and plugs (mainly because I don't know when the plugs were replaced last), reset CEL and it came back 3-4 days later with all of the codes:

P0421
Catalyst System Efficiency Below Threshold Bank 1 - Upper limit value exceeded, test conditions are not-completed, fault is currently active and causing a DTC light
P0431
Catalyst System Efficiency Below Threshold Bank 2 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and causing a DTC light

P2237
Lambda control adaptation at idle, Bank 2 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and is not causing a DTC light
P2237
Lambda control adaptation at idle, Bank 2 - No signal/communication, test conditions are not-completed, fault is currently active and causing a DTC light
P2235
Lambda control adaptation at idle, Bank 1 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and is not causing a DTC light
P2235
Lambda control adaptation at idle, Bank 1 - No signal/communication, test conditions are not-completed, fault is currently active and causing a DTC light

So I'm back at the catalytic converters again which I'm fine with doing, but here are my questions:

1. Do catalytic converters fail this soon on a low mileage vehicle?
2. Why would the P2237/2235 codes come back?
3. Any ideas on what I may be missing? More vacuum leaks, ECM issues, etc?

Lastly as a side note, when changing plugs, I inspected the coils and they all looked fine (i.e. no obvious cracks, wiring in good shape, etc) but I did notice small oil build up on the top of the plugs (none in the cylinders - plugs looked normal). Is that indication of a leaky valve cover gasket and would that be related to any of my issues?

Sorry for the long post - just wanted to be thorough. Any help or insight would be greatly appreciated. Thanks everyone...

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Several of the codes you noted indicate communications/test not completed issues with the sensors, so let's start there.  The Durametric system should be able to give you real time voltage readings for the sensors, as well as graphically showing how the voltages before and after the three way cat are preforming.  You need to look at those voltages and see if they are inline with specs, and how the voltages are moving.  I suspect you are going to find that some of the sensors are not reading, which could be a sensor issue, but more often in a wiring or connector issue as having multiple sensors fail simultaneously is very unlikely.

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Thanks for the reply.  I will check tonight with the Durametric,  Since all 4 sensors are new and it's happening to both banks could I have an issue is the wiring harness leading up to the sensor plugs?  Or could it be something else more centralized like the ECU? 

 

Any thoughts on the cats themselves?

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Thanks for the reply.  I will check tonight with the Durametric,  Since all 4 sensors are new and it's happening to both banks could I have an issue is the wiring harness leading up to the sensor plugs?  Or could it be something else more centralized like the ECU? 

 

Any thoughts on the cats themselves?

 

 

You are getting codes for lack of communications, so if you try the read the sensors with the Durametric, you will quickly find out if they are communicating as the Durametric will see what the DME sees.  Both side O2 sensor harness do come together into the main harness that goes to the DME, so it could be a loose connector or wire damage somewhere in the harness, but if the DME is reading the sensors, then they are connected properly.  The DME can also be faulty, but like the three way cats, DME's cost a ton of $, so you don't want to go there without reason.  It is also fairly rare for a vehicle to blow both cats at the exact same time unless something really ugly got into them, but as you have not commented about poor running issues, I don't think that is a viable possibility.  You could have also had a momentary DME "brain fart" where it thought it lost touch, but really did not.  If everything is working and talking to each other, I'd suggest clearing all the codes and see what comes back.  Sometimes these cars just throw a ghost code(s) that are not real, and don't come back.

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So I hooked up the Durametric and read the voltages for all 4 O2 sensors and the lambda values for banks 1 and 2.  The voltages started in the 4+ volt range and went down to less than 1 as the vehicle warmed up.  The lambda seemed to stay around 1 volt the whole time with very slight fluctuations as the vehicle ran.  It looked like everything was tracking at this point.  I cleared the errors this morning and the vehicle seemed to still run fairly well all day, but while cruising down the freeway at 63-65 mph this evening the check engine light popped up again with only the two errors:

 

P0421

Catalyst System Efficiency Below Threshold Bank 1 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and causing a DTC light

P0431

Catalyst System Efficiency Below Threshold Bank 2 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and causing a DTC light

 

I'm leaning even more towards faulty cats.  Should I try and read the live values on the Duramertic?  I honestly wouldn't know which values to monitor so if that's the case some guidance would be much appreciated.  Thanks all...

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So I hooked up the Durametric and read the voltages for all 4 O2 sensors and the lambda values for banks 1 and 2.  The voltages started in the 4+ volt range and went down to less than 1 as the vehicle warmed up.  The lambda seemed to stay around 1 volt the whole time with very slight fluctuations as the vehicle ran.  It looked like everything was tracking at this point.  I cleared the errors this morning and the vehicle seemed to still run fairly well all day, but while cruising down the freeway at 63-65 mph this evening the check engine light popped up again with only the two errors:

 

P0421

Catalyst System Efficiency Below Threshold Bank 1 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and causing a DTC light

P0431

Catalyst System Efficiency Below Threshold Bank 2 - Upper limit value exceeded, test conditions are not-completed, fault is not currently active and causing a DTC light

 

I'm leaning even more towards faulty cats.  Should I try and read the live values on the Duramertic?  I honestly wouldn't know which values to monitor so if that's the case some guidance would be much appreciated.  Thanks all...

 

I would check for the action of the o2 sensors before and after the cats.  Specifically, you are looking for one sensor to draw a straight voltage trace, while the other on the same side cycles in a sine ware like curve.  This is a descritption of what you should see, and while it is for a Boxster, the principal is the same for your vehicle:

 

ThreewaycatandO2sensoragingdiagnostics_z

 

ThreewaycatandO2sensoragingdiagnostics2_

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