If you haven't already, can you extract all the codes from the cars computer? I am guessing that you don't have an OBDII hand-held interface ( If you don't know what that is then you don't have one). do this:
1) get a pencil and paper
2) Put your key in the ignition
3) turn the key on but do not engage the starter of the car
4) turn it off
5) on then off then on again
6) that was on-off-on-off-on
7) count the flashes of the engine service light(there will be grouped flashes.
8) the last sequence will be 55.
Go to this site to determine what codes you have
http://minimopar.knizefamily.net/fault/index.html
This may zero you in in a hurry.
If you have done this and know that your O2 sensor is the only issue, I'd like to know that too.
Check out this Awesome link for a manual...
http://www.neon-owners.org/neon/tech...97/EPL_TAB.PDF