code p0420 and p0430, bad cat or bad sensor?

Question

I had a heater problem with my bank 2 O2 sensor. Replaced it and after a few days p0420 popped up. Tried using cataclean but still nothing. Tried clearing code and popped up after driving bout 50-70 miles. Now both 420 and 430 are on. 06 Hyundai sonata v6 glad 133k miles I only use mid and only high when I put fuel injector cleaner in about every 5-6k miles.

Answer 1

HI there

I think I would look at the spark plugs and the air filter. If this is running rich it might cause both converter codes. It's unusual for both converters to fail at the same time like this, and if it was a problem with the O2 sensors it would be both rear O2 sensors failing at the same time and one is new. So, It's possible there is a problem with the fuel mixture causing the problem in my opinion.