Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › 2003 Nissan Code P 0420 › Reply To: 2003 Nissan Code P 0420 May 10, 2021 at 12:36 pm #990504 college manModerator if your getting P0420 the o2 is telling you that the cat is not doing a good job cleaning the exhaust. The cat is on its way out.