Getting a trouble code P1404

First, let me apologize for my typo. The code read was P1401 (Not P1404).
The car is in Texas, with my son, and I'm in Louisiana, on vacation. I've sent him a message asking if any other codes showed up when he took it to Autozone; but, I believe that was the only code that came up. Just waiting on his reply.

Son said that the P1401 code was the only one that showed up. He doesn't remember any noise at all whenever he removed the gas cap. I asked him to drive it 10 to 20 miles, tomorrow, and then listen for noise while he removes the cap. I'll re-post whenever he gets back to me. Thanks.

P1401 I belive this is a EGR insuffcient flow detected trouble code. This could be a few things the obvious faulty EGR Valve. Bad Voltage reading from EGR Valve possibly even a build up of carbon that may be blocking the passages to that of the valve or even the block or intake depending where it is mounted.

FINALLY, got my son to check for noise when the gas cap (which he replaced) was removed after driving over ten miles. He said that there was no noise, at all. So, the tank neither has a vacuum, nor is it pressurized.

Finally got me, the parts, and the car in the same state! Replaced the evap canister, DM-TL, and the purge control valve and reset the codes (which showed P1401, P1709, and P0442.) Took the car to the gas station and it filled with no problems at all. One problem down! Son told me that the car now seems to have more power than it did before we replaced the parts; and, the codes have not come back, so far. Hopefully that will be all we need to do. Thank you for your great advice!