i own a 2000 Maxima with the ses light on for code 0420. I troubleshot per the nissan repair manual, and i narrow it down to the last 2 possible causes, re-programing of the ecm, or a malfunction of the 3 way catalyst. Assuming the re-programing does not fix, does anyone have any experience on replacing the 3 way catalyst, or any tips on where to purchase one? thanks