I just bought a 2009 G37 with 130,000 miles. It ran great during the test drive with no engine lights on, and ran great the day I bought it. Unfortunately the new car euphoria only lasted a day, the next day after I bought it the SES light came on and the car went into "limp mode". I took the car to the mechanic and he ran the codes P0430 and P0420. He said I needed to replace the cats saying they were bad but living in Cali, these things cost $2000. A little later I consulted a SMOG technician and he said that "bad cats" would not put my car into "limp mode" and that at 130K miles my cats should be fine, and that it could have something to do with the O2 sensors or bad wiring or something like that. I also think that it is a weird coincidence that both codes would pop up with two bad cats.
Does anyone have any experience with these codes? Should I try to clean out the cats, or am I doomed?

 

I had this code pop up on my ‘10 Accord V6. Replaced sensors, still got this code although infrequently. It shouldn’t go into limp mode, (my Honda wouldn’t go into eco mode on the highway with CEL set) I hate to say it but best way to remedy this is to wait again till the codes come back, confirm they are the same and if yes, it’s the cats.

420 and 430 codes indicate the efficiency of the cat is below the manufacturers threshold. In a sense the code means cats are on the way out