I have a P0420 code on my VW CC 2010 and I've narrowed it down to a faulty catalytic converter.

I have edited this photo to try and explain easier. VW CC 2010 Exhaust

In the red circle is the catalytic converter I want to replace with a mangaflow generic from Autozone. I think that will solve the issue.

In the green is what I'm not sure if needs to be replaced. Is this another catalytic converter?

What is the name of this green and red parts? I asked for a quote on yelp and I had a guy tell me my car has 2 catalytic converters. In the blue there are two oxygen sensors. The dark blue one (downstream) i've replaced before. I'm not sure if I should replace the light blue one.

Apologies for all the questions. I'm really trying to learn here and hopefully make the best purchase for the fix. I will read all replies. Thanks!

2 Answers 2


Your mechanic may be right, or at least think he is. For Engine code CCTA, there are two converters - one in the space of that "lump" in the left side of your picture, and the so-called "center" converter. The primary converter probably isn't large enough to handle the whole cleanup on the turbo CCTA engine.

That may not be the right picture for your vehicle. Below is the exhaust system for the CCTA engine, showing the O2 sensor bungs right at the turbo flange, and the downstream sensor (wide range six wire) after the center converter.

Alldata even depicts some variants with three O2 sensors on the ECU, but I could not find a physical picture to prove it.

Check around the turbo flange to see if there's an O2 sensor there. In that case, I'm pretty sure there's a catalyst honeycomb in the barrel "lump" after. (But SolarMike is quite correct; the item in your green box is merely a flexible joint.)

In any case, P0420 comes from information from the last sensor, or the one located after the center catalyst. FWIW... There's really no telling which single converter is causing the problem, or maybe both, or maybe the P0420 is caused by 100 other things that seem to indite the converter(s), but are actually due to A/F ratio issues that deplete the oxygen storage. It might even be due to a failing O2 sensor.

If you are certain you have the O2 sensors only in the locations you describe, you may have the CBFA engine varient, just one converter, and your "yelp quote" mechanic hasn't done as much homework as you have. I suspect the latter.

Good luck!

enter image description here

  • Awesome information. Thanks for the picture. I don't have access to fancy repair stuff like alldata so i do appreciate you helping me out. Seems like my best bet is to replace all o2 sensors and move on from there. Commented May 14, 2019 at 20:39
  • I checked for the o2 sensor near the turbo and it's not there. Also the cat looks a lot more like the picture I uploaded than the one you sent. So it is confirmed does my car only have one cat? Commented May 14, 2019 at 22:33
  • Your best bet is to watch the secondary (post-cat) O2 sensor data on a hot cat with a good graphing scan tool. If it makes sense, you may have a bad converter. If it is erratic and doesn't follow the same shape as the upstream (pre-cat) O2 sensor, you may have a bad sensor. I hesitate to thrown costly parts at an unknown condition.
    – SteveRacer
    Commented May 15, 2019 at 8:42

I would suggest that the part you have in the green box is the flexible joint designed to absorb engine movement so that the rest of the exhaust does not move so much.

The cat has the oxygen sensors before and after it, ie the part in the red box.

  • My confusion had started when a shop mentioned my car had two catalytic converters. He said "Hello Salvador, are you wanting to replace the front converter or the middle converter your car has 2". If that flexible part is not a catalytic convert then he is incorrect. Commented May 8, 2019 at 20:49

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .