2.8 V6 Oxygen sensor ?

["C. Krafft" <ckrafft@olg.com>]

I have recently had a recurring engine warning light come on in my 93
100CSQW.  Checking the engine code (by shorting the correct pins) reveals
code 2331 which according the the info from the 12V troubleshooting pages
is the oxygen sensor.  Question is, where is this sensor located?
Also, have unrelated error code on Channel 1 on the temperature control
diagnostic 13.7 and 11.7, and sometimes  11.5 too, I think.  Code look-up
says something about a stuck flap.  Anyone have suggestions on how easy it
is to access this (or to clear codes if problem is gone).  First noticed
problem after driving through a terrific downpour - sounded like lots of
water was slushing around inside the ductwork.  Don't here the water
anymore, however error code is still there.  
Thanks,
Charles Krafft