2002 Ford Escape Question: I have a check engine light on and diagnostic says B1S2 sensor. Where is it?

02 Ford Escape 3.0l B1S2 oxygen sensor. I 've gone to 4 different mechanics some say before and some say after the catalytic. I've changed out 1 after the engine going toward the muffler I dont see any sensors after the catalytic. The check engine keeps coming back after cleared with the same sensor error. The last mechanic I saw after installing the new sensor said the one by the radiator needs to be replaced. I located it but cant reach the other end of the cable. I moved the battery out of the way. Where is it located and how can I replace the B1S2 oxygen sensor?