1999 Honda Civic Oxygen Sensor

Hello all. Recently my Civic was taken in for Diagnostic because the
check engine light came on. The Honda Dealer told me it was the
secondary Oxy Sensor that needed replacing. They wanted $480.00 for
the parts/labor (Ouch!). I decided instead to buy the replacement part
at NAPA and did the job myself. After completing the job the check
engine light went out for five minutes then came back on.

I then took it to the Dealer and they reset the cars computer and the
light went back out again for five minutes. They did this twice and
told me I must have gotten a bad part from NAPA. I exchanged the part
with NAPA, reinstalled it, and still have the same problem.

Should I take it to the dealer and try to have them reset it again?
Has anyone else had this problem and if so what's the fix. Thanks for
your help.