0303 or P0150 code, O2 sensor

This code was thrown after my car has started to act up , stalling at a stop and running poorly, .. It says its the Front left heated O2 sensor, .. anyone ever replace this? if so could you let me know what the deal is..

It's the O2 sensor in the first part of the Y-pipe. Order a new one from www.oxygensensors.com and it's very easy to replace. Check the Maxima.org forums for directions (I wrote the 4th gen directions)

~THT