O2 sensors on '98 Explorer 4.0 V-6?????

[K's explorer]

The check engine light (CEL) has been coming on in my 1998 Explorer, 4.0 V6. Then after a few days it goes out. I checked the codes and it shows 0153. This comes back as O2 sensor circuit slow response (bank 2 sensor 1). After erasing the codes it comes back with the same thing a few days later. I know this model Explorer has three (3) O2 sensors. The problem is where are they located and which one is "Bank 2 Sensor 1"? Even my Chilton manual doesn't show where these sensor are located. I'd rather just replace the sensor that's going bad.
Thanks for any help anyone can give me.

 

[BradE.]

Drivers side O2, before the cat on the exhaust y-pipe coming down from the motor. The sensor will be screwed into the pipe and have an electrical lead and plug that runs from the sensor to a connection by the tranny.

 

[tpg]

How in the world do you GET to the connector? Tightly packed between the engine and firewall.