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 ?

What brand O2 sensor did you use?

The sensor I used and the one the shop mechanic installed were both Denso brand . The first one I put on was a different brand but do not remember brand used .

sometimes its the connection, instead of a problem with the sensor, unplugging it and plugging it in makes it work a while

I'll try that and see if it will make it work . Any idea what will happen if it is simply ignored and continue to drive with the light on ? It does not seem to effect the car running well .

the o2 is extremely important for fueling, if its for the upstream one. if it runs rich it can plug your new cat. if its lean it can damage the engine. if its for the downstream one that only check the state of the cat

It is the upstream sensor . I can not change the sensor every month or so . Has to be an answer to this somewhere .

inspect the connector and wires

Have you pulled the sensor and looked at it for contamination? Otherwise check the harness connectors(drag test) or check the harness for chafing/grounding out.....