If it is the O2 sensor code again, install a ground strap from the head of the affected O2 sensor (right front one, I'll just take a wild guess) and attatch it to the intake manifold where you'll find a couple of other grounds being bolted. Lower intake, I believe.

There have been many a time where a poorly grounded engine has developed bad O2 sensor codes. Replacing the sensor won't fix it, adding grounds will.

Also, double check all of your O2 sensor connectors. They'll all be on the right valve cover. Check them for corrosion and for water intrusion. People that wash their engines have trouble with water getting into the O2 sensor connectors.