I recently bought a 98 TJ 4.0 and the check engine light came on. When I went to Autozone and got them to read the codes, P0455 and P0463 came up. They cleared the codes and sent me on my way saying that it might be the gas cap or a leak somewhere. I then tried to get it emissions tested and it failed. The gas cap is on tight, does it need replacing? Also, is there a leak in the system somewhere that would need fixing to pass emissions? Any help on the codes is much appreciated.