Wouldn't that be nice, to flash the ECU? Unfortunately, our ECU isn't flashable, so you have to buy a new one, with new logic, and a new part number. Even a new ECU doesn't guarantee a fix, because the catalytic converter(s) may still be bad. (See
http://ww2.justanswer.com/uploads/sn...3701_p0420.pdf ).
Hopefully, you're not due for an inspection soon. As long as P0420 is your only code, you don't have to worry about damaging your engine, so you can continue to learn, then try the cheap-fix ideas, before having to bite the bullet on a big repair. But, if you have an inspection coming up, and if it includes emissions, you will fail with the CEL on, and you will not pass unless your readiness monitors are mostly "ready."
