My 2005 Buick Century with 353k miles gets a recurring P0420 code, catalytic converter operating below efficiency level. Twice this year, I tried using Cataclean, but with no success. I noticed a small hole in my muffler at the seam. Could a lack of exhaust back pressure cause the CC to operate inefficiently or improperly? Can anyone recommend a catalytic converter cleaner? Or, is it all snake oil?
No, lack of backpressure has nothing to do with your issue.
You need a new catalytic convertor most likely
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the muffler is after the catalytic converter. So a hole in the muffler isn’t going to effect catalytic performance.
I know people go into denial, (and I ain’t talking the river), when this code appears, but in all the years being a mechanic this code always meant the converter needed to be replaced. Especially if the vehicle has over 300,000 miles.
You just need to hook a scanner up and watch what the #2 O2 sensor is showing to confirm if the cat is bad.
Tester
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Yeah, likely the cat. How many miles do you go between adding a quart of oil?