Dear Scotty, love your knowledge. I have a 2003 VW Passat 1.8t with 135k. Runs like a champ. However, I've been logging the mileage between code intervals which is about 300 miles each check engine light with this code. I needed to pass inspection in September and had a hole in the exhaust pipe midway back between the one cat and resonator. I had to remove the cat at the turbo to fix, weld the new pipe in place. So with new flange bolts re attached the cat and pipe in place. No problems. The cat honeycombs all looked clean on both ends, in and out. But since that, it is tossing up this same code every 300 miles. I did a thermal test and the cat appears to be now bad as heat is lower and out than in. Some say this is a problem. OK, so why all of a sudden? This will be the death of this car as Cats are way too expensive, and junkyards in NY cannot sell to us. Is there no additive that would clean a cat?? Thank YOU, Paulie
You can try a bottle of CataClean, available at any auto parts store.
https://www.holley.com/products/cataclean/cataclean_-_fuel_and_exhaust_system_cleaner/parts/120007
However, at that age and mileage it is likely the converter has indeed failed. They are definitely expensive, so I would not blame you for looking for another vehicle. Cat failures are very random, so there is no telling exactly why it chose this point to go out.
Thank you
Are you sure it’s the cat? See link below for possible other causes:
https://www.obd-codes.com/p0420
And see video for how to tell if it’s the cat or not:
https://m.youtube.com/watch?v=9VZ5K8n5jj0
I’d look at some data if you have a scanner, not a guarantee that the cat is bad.
Thank you.