Re-hash of info

Ok, new to the forums but watch a lot of what is said. Want to reopen an issue that I have now and am looking for a bit of help. Have an 06 Frontier SE 4x4 with the 6 spd manual. Yesterday I got the P0448 code when the SES light came on. Checked everything that was listed on the current posts in the forum and unfortunately nothing has worked to clear the code or the light. Started with the gas cap, simple and easy and a number one suspect on a lot of vehicles. Nope, not that. Checked the lines, hoses, electrical, box, etc and nothing is amiss. The other forums on this issue show that there is a gas smell (none here), poor performance (again nothing), spewing of fuel and fast pump shutoff (not with this one). Everything would point to these issues to create the DTC but none of them are on this truck. Possible malfunction of the PMC (hope not cuz that will be a fortune to replace). My poor buddy could use the help on getting himself fixed, did I say that he had 196K on the clock and this is the first for this? Thanks for any help.