Nissan Repair: failed smog chek/ suggestions for at home repair., oxygen sensors, catalyst system

Question
my 2003 nissan sentraGXE just failed a smog check.  reason given was: catalyst system efficency bel.  what is this, and can I fix it at home?  If not, is repair expensive?

Answer
can you be more specific "catalyst system efficency bel"...i think part of your sentance was cut off.  if i can take a guess at what the rest of the part is, ..below level? if thats the case, try reseting the code in the cars computer.  if that doesnt fix the problem you may need to replace the catalitic converter and/or oxygen sensors.  i hope reseting the ecu helps, otherwise you will have to spend some $$$.  best of luck to you!