I have replaced the front lower oxygen sensor 3 time what else may cause it to fail

What is your question?

I had replaced the lower front oxygen sensor three times, but still, the engine light comes back, giving the same code. I even took it to Ford dealership mechanics. They could not figure out why other than replacing it again and charging me double the original cost. Does anyone know what or why I'm having this issue?

What makes this problem better or worse?

I unable to pass the emissions test

How long has your 2004 Ford Escape had this problem?

6 to 9 mounths