cordsig79

I found these OBD II code errors on other sites....just asking if anyone has every replaced 02 sensors or if this is common?

I think sensors are much cheaper than if its a catalytic replacement.

2006 Base

Catalytic thermal issues....

1 fuel air mix ratio too high

2 air leak in catalytic system.

911SLOW

Probably (90%), it's one(or more) of the oxygen sensors..

cfiiman

Bringing up an old thread b/c I have the exact same issue and was just wondering what you ended up doing with yours to fix it? Was is the 02 sensor(s) or a Cat? Any issue would be appreciated. When I bought the car is was a "stored" code and have driven several hundred miles with no CEL, today it came on letting me know the issue is still relevant, thanks for any reply!

cordsig79

I notice when temperature changes happen.....winter into spring and Fall into winter....the Temperature changes cause an imbalance in the mixture it's reading and it fires the code. If it returns to the previous temperature it was used to running the code comes off fast or if it maintains, the code goes off after about 4 days.

Cleaned MAF, then Replaced MAF just recently......DO NOT REPLACE the O2 sensor Or Cat's they are expensive and intensive.

My buddy is Head tech @ another German car company after market sport shop and he said they have a guy who sprays a mixture into Cats for about $300 to clean and restore them, it's a better option to try at first over replacing.

cfiiman

Yeah mine definitely seems intermittent. I had it happen on a honda (similar code) and it would come on and off for years but never stayed on. I replaced the O2 sensor in it and that cleared up the problem completely.

cfiiman

Going to resurrect again b/c I got a chance to get some live data from my 04 Base Cayenne today with my new Durametrics cable and laptop. I know these are Cat codes but since it could also be something else (bad 02, etc) I decided to record some live data to look at. I'm very new to Durametric and used it to capture the below values and exported it to an excel file. It is about 2.5 minutes worth of data and I wasn't sure exactly what to select in Durametric so I tried to get what I thought was appropriate to diagnose what exactly is going on. The Values I selected were:


1. Exhaust Temp Ahead & After CAT
2. O2 Sensor Voltage Downstream Bank 1 & 2
3. Status of Catalyst Bank 1 & 2

I may be putting too much emphasis on temps, but based on the inlet/outlet temps of the CAT, I'm wondering if that is showing me the answer? At the beginning the inlet temp was lower but not by a ton, then midway through till the end the outlet temps were lower which I think is a sign the cat is not working correctly. I think the O2 readings appear ok since they don't jump around to much and stay around the .5V figure with mainly .6-.7 being the most common in the data stream which is where downstream O2's should be correct? I have no idea what the Status of Catalyst is and was hoping someone could clue me in. I selected it b/c I "thought" it might be important but the value is solid throughout not sure if that is good or bad or what or if it even tells anything.

I'm trying to plan my course of action which I've game planned to a few different things depending on what the data tells me:

1. Maybe the CATS can revived with a chemical cleaner (doubtful). I know that these codes will throw if the cats operate at less than 95% efficiency, so maybe mine is only slightly below that and can be cleaned a bit, but the temperature data difference at the inlet vs outlet is making me think this might be a waste?

2. New O2 sensors. These aren't too expensive but I hate just throwing new parts at something without something to back it up. From the data stream it didn't look like they were too out of wack but maybe I'm missing something, I've certianly replaced them in other cars when I was having CAT codes and that corrected the problem so...dunno.

3. New CATS. I've found some reasonably priced aftermarket OEM fit/finish replacements from a company but hate to get into that if any of the easier stuff might work.

4. Go all ghetto and put an anti-fouler in the downstream O2's to get the light off (last resort).

The car runs great and getting around 18 mpg in mostly city/some hwy, so that seems normal. Just need some advice for those of you that know Durametrics well, and can help a member out by looking at the excel data file. If I missed some important data that I needed to log please tell me and I'd be happy to go data log whatever you all think I need to, again I'm new to Durametric and there are so many options I was a little overwhelmed and went with my "gut" feeling. Anyway thanks for any help, here is the exported data from Durametric:

2004_Cayenne_Durametric_Export

cordsig79

I would say that if you start proactively fixing things, you'll go down a rat hole. Now if it's something causing an inspection issue or what not, then I would say ok this time.

I would use durametric to remove/clear codes and double check it is not something new I have ever seen before clearing.

Something will come up, and you'll need that proactive budget for a reactive issue.......I the biggest things I have done were the transmission control valve replacement, and the gasket replacements...prior to that fuel pump number 1.

Other than that it's been oil, gas, and tires to go down the road.

I would just keep it clean with good oil, maybe send off the to Blackstone labs.

I am @ 180k miles after acquiring it new in 06........and I think i have extracted all the value I could want out of this little piggy, Ill be parking it soon for my newborn to pick up when he is 14-16 years of age.

wrinkledpants

I'm 95% sure it's the oxygen sensors. You don't often hear about failed cats.

If it's sensor 1 (bank 1 or 2), these used for the actual tuning of the car. They have built in heaters that can cause them to fail over time. Or, they just start having erroneous readings. Sometimes the sensor will fail and cause the code, or sometimes the cat readings will cause the code. The sensor 2 readings are from the second set of o2 sensors, and those are purely for emissions purposes. You could drive around all day and not have the car run adversely with these codes. If you won't want to be looking at a CEL all the time, replace both of whatever sensor is tripping the code.

matthew_brady

Since this is one of the top results on Google when searching for Cayman P0421, I figured I would bring it back to the top as I, too, am now experiencing this code from time to time.

To troubleshoot, I swapped the front O2 sensors side to side. Doing so should raise the P0431 code, I believe, if the O2 sensor was the faulty part (same error, other bank). However, the code remains P0421. Could it be that this indicates a bad catalytic converter? I have read elsewhere that P0420 (Catalyst Efficiency Below Threshold) is the code that's typically associated with a failing cat.

With the cats being as expensive as they are, I was hoping maybe someone can confirm or deny that the P0421 code can indicate a failing converter, before I dive in replacing things that don't really need to be replaced.

Car is an 06 Cayman S, for reference.

J'sWorld

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matthew_brady

Ah, I thought that might be the case, but had read that the rears don't do much from an emissions perspective?

I guess I'll swap those side to side next and see if that isolates the problem. Thanks!

J'sWorld

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quip11

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.

deilenberger

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.

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.

iCarScan can graph these outputs. I suspect Durametric can do the same.

Fixing things by throwing parts at the problem without any diagnostics to isolate what parts actually need replacing can get expensive - fast. An iCarScan costs less than $200. How much did needlessly replacing the pre-cat O2 sensors cost?

quip11

Thanks @deilenberger!

I guess I will be looking for that iCarScan or Durametric if I expect myself to be diving into this DIY (which I enjoy). Curious if you prefer one over the other?

Thanks again!!!