2003 altima

I have 2003 nissan altima w/ 113,000. miles on it, I have a trouble code "P0420 three way catalyst function" or "catalyst system low efficiency" What is wrong what do I do to correct the problem is it the catalytic converter or what.
thank you in advance for your help!!!!!
PIETRO

I think this link answers your question. Try resetting the ECM.

Check for unlimited mileage warranty. Several vehicles need an ECM flash to correct the problem.

http://www.obd-codes.com/trouble_codes/generic/p0420-catalyst-efficiency-below-threshold-bank-1.php

I think this link answers your question. Try resetting the ECM.

Check for unlimited mileage warranty. Several vehicles need an ECM flash to correct the problem.

http://www.obd-codes.com/trouble_codes/generic/p0420-catalyst-efficiency-below-threshold-bank-1.php

Thank you for info, I already had reset ecm but light came back within 36 hours, (I drive 200 miles a day). the web site is very helpful, I will try these options I should have known the o2 sensor is first line of attack.
thank again
Pietro