I have an 03 Sedan (Auto). My Check Engine Light just came on while driving home, despite the car seeming to run fine. I brought it to AutoZone for DTCs. Here are the codes it gave me: P1614, P1615, and P0442. Looks like the chip in the key isn't recognized by the ECM; however, I started it with my other key and the light still came on! I called Nissan, and they were basically no help. Any replies would be greatly appreciated

P0442 is an EVAP code, could be something as simple as a loose gas cap. The other 2 are for the immobilizer, not good at all. If you keep getting that code the car will eventually become locked out and you won't be able to start it. If your sedan has an ECU that is tuneable with Uprev the cheap and easy answer is to simply flash it with Uprev and disable the immobilizer, if not its a hope and a guess and lots of $$ trying to figure out why its malfunctioning

Do you have a second key? If so I would switch to that key and use it for a few weeks then scan for codes and see if the immobilizer ones have self-cleared.