Okay, so my wife's '03 Corolla has about 103k miles on it and since about 80k has been intermittently throwing Code P0420: Catalyst system efficiency below threshold (Bank #1). I know that it means there are four possible causes: leak in the exhaust system, faulty sensor before the cat, faulty sensor after the cat, or the cat has failed. We had the light reset after it came on at 80k and it was good for ~10k miles. Then it came on again. Then it went off again. Then it came on and has stayed on for about the past 6k miles. Before trying to fix it, I googled the code and found reference to a Toyota TSB #02804 referencing this code that seems to say a computer update is needed. I called the local dealers hoping someone would say "Yeah, since that TSB went out - go ahead and bring it in we will update the computer free of charge and see if that fixes it." What I actually got, even after describing it as intermittent and mentioning the TSB, was "Your Catalytic Convertor is probably bad, you are probably looking at a $2k repair. Bring it in and it will be $100, we will run the codes and work up an estimate for you - but I'm warning you it will likely be $2k." If we didn't need it to pass emissions I would just keep driving it. Add to that the fact we have been thinking about selling this car for about a year now. Questions: can independent mechanics update the software like that TSB seems to say should be done? Are there any magic words I can say to the dealer to force them to just do this update so I can do the work myself? Thanks for any help guys.