The wire doesn't unplug at the sensor. There should be a connector a few feet up the wire along the firewall.

 

Yeah if it's the bosch system it detaches near the master cylinder, one plug for the two white wires and another for the ground. Removing the sensor from the down pipe is no picnic, I had to use a slotted box end 22mm (to get around the wire) some heat and some penetrating oil, then lots of cursing.

 

Or you could do what I did and cut the wire then a few weeks later post a question to the board " does anyone recognize this connector"

 

I used wire cutters, worked like a charm