VW CC 2010. Catalytic converter was replaced when I first got the car at 78k miles. It is now at 83k miles. Downstream oxygen sensor was replaced at 80k miles. There is a small leak in the catalytic converter.I'm only able to see it because carbon buildup has accumulated in a spray/dam pattern from the hole. Obviously it is leaking exhaust from here but could that be the culprit for a p0420? The other option I have is to replace the o2 sensor I doubt it's the catalytic converter since it's almost new..

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  • Where is the hole in relationship to the O2 sensor? If it's very near it, it very well could be causing the P0420. If the computer thinks there's too much oxygen in the system, it will think the cat isn't doing it's job. The O2 looks for oxygen and not CO2 or other exhaust gasses. Even though you're seeing carbon tracking, it can still be drawing in oxygen through the hole. Apr 12, 2019 at 21:26
  • Was the new converter aftermarket or oem? Keep in mind that converters don't usually self destruct. They fail due to a less than ideal exhaust such as oil consumption, coolant, excessive rich condition, and ignition misfires to name a few. As Paulster said, it could also be drawing oxygen in at the leak, skewing catalyst efficiency.
    – Milison
    Apr 13, 2019 at 0:08
  • I've identified that the hole is downstream from the catalytic converter and plugged it up with some exhaust putty, cleared the code and it still came back. I've attached my o2 sensor info in my post. Can anyone help me interpret the data from my obd2 scanner? Apr 15, 2019 at 21:49


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