In January 2007 at 53,769 miles, the check engine light in my '05 2.5i wagon (PZEV) came on, and it threw a P0420 code (cat converter efficiency below threshold). Both cats were replaced under warranty at that time.
In November 2009 at 104,882 miles I had the WVH18 ECM reprogram done. (according to the letter from SOA, the ECM needed to be reprogrammed because under certain driving conditions, the cats may develop hi temps that exceed design specs).
The other week at about 145,250 miles the CEL came on while driving on the freeway, and stayed on for the next 1000 miles or so. I hooked up an OBD-II reader which showed the P0420 code. I didn't reset it. Today - for no apparent reason - the CEL stopped illuminating and the cruise control stopped flashing. I hooked up the OBD-II reader again, and it still says P0420.
I have an appointment at the stealership for next Tuesday to check out the CEL issue. But now the CEL is no longer illuminating, yet the P0420 code still shows up in an OBD scan.
The fact that the P0420 code is still present - does that mean there is still something going on with my cat (that's not bad enough to cause the CEL to come on), or does it merely mean that the cat problem has resolved itself and the code just stays there until it's reset?
I kind of want to have it checked out at the stealer, because if something's wrong with my cats, I'm very close to the PZEV emissions warranty running out at 150K miles. However, they charge $100 to diagnose CEL problems. if they're just going to tell me that since the CEL went off by itself, everything is all good and the code just needs to be reset, I can reset the code myself.