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Hello all! Apologies for taking this tread back up.
I recently purchase my new to me 08 GTS last June with about 122790 miles when I took it home. CEL came on a week later. I do not have a Durametric but my regular scan tool revealed P0421 and P0431 codes. I cleared the codes to see if it will come back and started searching for the possible causes. I've driven the ute sparringly and the CEL have come back since.
First thing I did was purchase the front O2 sensors. Had it replaced with the help of my son who happens to work for a VW dealer in my area. I cleared the codes again, only to come back again shortly before getting home.
I've recently purchased the back O2 sensors but haven't installed it yet.
After searching and reading and talking to a few mechanics about these codes, I'd like to believe (wishful thinking) that it's also just the O2 sensors (as wrinkledpants suggests). Does anyone have any other reason on why it shouldn't be? Have anyone heard or experienced a failed cat at this mileage?
My son have consulted some of his fellow mechanics at the VW dealership and was told that the cat needs replacement and NOT the O2 sensors.
Any of your thoughts and expertise regarding the matter is highly appreciated. Thank you.
I had to replace my P/S cat at 80k miles to clear a P0421, so at 122k miles, it is certainly possible that it has failed...
I had to replace my P/S cat at 80k miles to clear a P0421, so at 122k miles, it is certainly possible that it has failed...
Thanks Matthew. That certainly is a BIG possibility I'm facing at the moment. Not sure if there's any state law that will prevent me from doing the work myself, especially being in CA. Where did you get your replacement cat, if you don't mind me asking?
Thanks Matthew. That certainly is a BIG possibility I'm facing at the moment. Not sure if there's any state law that will prevent me from doing the work myself, especially being in CA. Where did you get your replacement cat, if you don't mind me asking?
I bought a Magnaflow unit and replaced it myself. I don't know if what I bought was CA compliant though.
Most CTT P0421/P0431 Cat inefficiency codes are due to unburned oil, blowing through from the crappy PCV system. Clear them out and run a PEA-based(Polyether Amide) fuel system cleaner to "rinse" the cats clean, while doing the "Italian Tune Up."
This is a case where having the correct scan tool might save you unnecessary parts expense and labor.
If you have a decent scan tool - you can plot the output of each O2 sensor, and you can tell if it's working correctly by the output pattern.
I ordered the x431 to your point. Thanks for the suggestion.
Most CTT P0421/P0431 Cat inefficiency codes are due to unburned oil, blowing through from the crappy PCV system. Clear them out and run a PEA-based(Polyether Amide) fuel system cleaner to "rinse" the cats clean, while doing the "Italian Tune Up."
Thanks Dilberto! Would Techron qualify as one of these fuel system cleaner? Would 1 bottle per fill-up suffice? And forgive my ignorance.. What is "The Italian Tune Up"?
Hi Don. Finally got around to activate iCarscan and plug it into my Cayenne. I suppose the lambda plot example you showed is from a different scanner. I performed a full health scan. It didn't give any plot scan but a bunch of readouts.
I apologize, I didn't expect the images to be so large. So while I only got the P0421 and P0431 previously, which made me replace the pre-cat O2 sensors, this actually gave me additional 4 more. I hope you can give me some advise on how to proceed. I took screen shots on all after I ran the health scans. I just don't know what to post. If you find the time to let me know what you need to see to complete the picture, please let me know. Thanks!!!
I'm not that sure what that combination of codes is telling us. The P0421/P0431 codes tell us the cats aren't kicking off as quickly as the ECU would like. On a cold temperature startup a 955 will fire off the auxiliary air pumps (the ones located over/behind the valve covers on the firewall) to try to get the catalytics to kick off and work more quickly. These don't go off if the temperature is warm enough (I seem to recall around 40F or so, but don't take it as gospel.)
The P0660 - dunno. Never ran into that, and can't really think of what device they're talking about. Hope someone knows..
P2181 - too vague. Has it ever overheated..?
The two about air-mass may be referring to the MAF's - which have been known to fail. Unfortunately - it's not telling us which one it thinks is wrong.
Dunno. I'd first try clearing all the fault codes and driving it to see if they reappear. Spurious codes are certainly not unknown, especially under low battery conditions (has that happened?)
I'm not that sure what that combination of codes is telling us. The P0421/P0431 codes tell us the cats aren't kicking off as quickly as the ECU would like. On a cold temperature startup a 955 will fire off the auxiliary air pumps (the ones located over/behind the valve covers on the firewall) to try to get the catalytics to kick off and work more quickly. These don't go off if the temperature is warm enough (I seem to recall around 40F or so, but don't take it as gospel.)
From your experience, Is there anything from these codes that suggests the cats needs replacement? I already bought the post-cat O2 sensors but held off replacing them after reading your initial post. Thank you!
P2181 - too vague. Has it ever overheated..?
I've never seen the temp go up to abnormal level, although I only drive it sparringly. Approximately 2200 miles since I got it last June.
The two about air-mass may be referring to the MAF's - which have been known to fail. Unfortunately - it's not telling us which one it thinks is wrong.
Are the MAFs interchangeable from each sides? Maybe I can try to switch them and see if I get the same codes?
Spurious codes are certainly not unknown, especially under low battery conditions (has that happened?)
I do not know when the battery have been replaced last. I suppose I can get under the seats and hopefully the stickers somehow shows when the battery was installed.
Thanks Don for your time. I'll clear the codes and see what comes back.
Hi Don. Finally got around to activate iCarscan and plug it into my Cayenne. I suppose the lambda plot example you showed is from a different scanner. I performed a full health scan. It didn't give any plot scan but a bunch of readouts.
I apologize, I didn't expect the images to be so large. So while I only got the P0421 and P0431 previously, which made me replace the pre-cat O2 sensors, this actually gave me additional 4 more. I hope you can give me some advise on how to proceed. I took screen shots on all after I ran the health scans. I just don't know what to post. If you find the time to let me know what you need to see to complete the picture, please let me know. Thanks!!!
Pretty sure P0660 is for the electric changeover valve for the tuning flap in the intake manifold. If the intake manifold has been off recently make sure that got plugged back in. With P0421 and P0431 you probably need cats but to really know for sure you need to plot out your rear o2 sensors, like deilenberger mentioned. P2181 is for your thermostat. P1084 and 1091 make me think you have some kind of air leak.
Pre-cat O2 sensors have a sawtooth/squarewave sort of pattern as the ECU switches from rich to lean to rich to.. a failed sensor in this case won't show the switching, or show slow switching. Easy to spot the bad one once you know what you're looking for.
Above is a plot from a scan tool I use on my motorcycle - showing the switching from lean/rich/lean/rich for both cylinders of the motorcycle (BMW twin - with a sensor for each cylinder.)
The post-cat 02 sensors should show a basically flat-line at a set voltage. That means the catalytic converter is working correctly. If it shows a pattern of rich/lean - that means the catalytic converter is no longer working. If it shows a 0 volt pattern - that means the 02 sensor isn't working
Hi Don. Based on your explanation above, if I understand it correctly, the post-cat readings is opposite of the pre-cat readings, right? As you know, the iCarScan does not plot graphs, only values. Here it is. Thanks for your time and everyone else. Looking forward to your inputs!
Is this the graph counterpart?
I'm presuming the top two on the list is the Pre-Cat sensor and bottom two are Post-Cat sensor readings?
I'll have to hook mine up and see where you're getting those.. and I don't understand it not plotting graphs - mine offers to on almost any real-time data.
10-12-2017, 01:46 PM
