Welcome to JustAnswer.com! My name is DriveFast71(Ron) and I will do my best to answer all of your questions completely and accurately.
The P1457 is a "known problem" and Honda has issued a Technical Service Bulletin that states the problem is going to be in the EVAP Bypass Solenoid. If the solenoid is replaced, and the problem still exists, in a few rare cases, the PCM will need to be replaced as well.
January 28, 2003
MIL Comes On With DTC P1457: EVAP Bypass Solenoid Valve Failure
The MIL is on, and DTC P1457 [leak detected in EVAP control system (EVAP control canister system)] is set.
The EVAP bypass solenoid valve can fail due to corrosion. The solenoid valve may get water inside. If the water contains road salt, the solenoid windings could corrode, causing the valve to fail. In a few rare instances, the corrosion could be severe enough to cause an internal short in the solenoid valve, which could damage the ECM/PCM. If this happens, both the bypass solenoid valve and the ECM/PCM would need to be replaced.
Test and, if necessary, replace the EVAP bypass solenoid valve. Replace the ECM/PCM if needed.
Yes. This is true with just about every code (depending on which system has the fault). When you clear the codes, the on-board computer needs to "reboot" and re-check all the systems. The EVAP system is low on the list of systems to check, so the light will remain off usually for about 50-75 miles, or until the on-board computer "re-recognizes" the problem after reboot.
It's located under the vehicle, mounted to the side of the EVAP Canister. If you click "View Full Image" on the image I provided above, you'll get a pop-up window with a close-up view.