O2 sensor issue.
I have a similar problem . Replaced upstream sensor , down stream sensor , the catalytic converter . Light still comes on . Took it to a repair shop . After two trips there , they replaced the upstream sensor that I had just put on . The light went out for about 10 months and came back on . Replaced the upstream sensor again and light went out . About 1500 miles later light came on again . What is going on ? Any ideas ?