I got the code pulled, P0140 bank 1 02 sensor. I have a Stillen y pipe, does this have to do anything with it. What can i do TO fix this problem. If i was to buy a new 02 sensor and replace it will i still have the same problem or will it take care of the (SES). Thankz

 

http://maxima.theowensfamily.com/tsb/NTB02-051a.pdf
It probably has more to do with the ECM than the Y pipe. See if you still fall under this TSB. You might be able to have it done free if your warranty is still good.