Idiot Light 'Check Engine Light' [Code:P1456]

I was driving home from work last night when I noticed the CEL came on and stayed on. I pulled over and checked the oil level and antifreeze, and all fluid levels were OK. My car just passed Virginia emmissions last month. I read the code today and it came out P1456: manifacturer auxilliary emissions controls ( I think). Does anyone know what this code is pointing to? Does replacing the gas cap fix this issue?

Thanks for any comments and thanks in advance for your time,
-Mott

2002 Accord EX-L 5 speed 139K miles

That IS the code you would get if your gas cap was loose.  Actually the code says:
"EVAP system leak - fuel tank system"
 
Which really means that something on your gas tank is not airtight like it should be.  The most likely culprit would be a loose gas cap.  Other possibilities would include...
 - Gas cap gasket is bad so it leaks even when tight
 - Leak in the fuel filler pipe or that group of hoses
 - Fuel pump mounting flange gasket is leaking
 - A leak in any of a dozen rubber hoses & stuff around the tank or in the engine compartment
 - An actual leak near the top of the gas tank
 - - (a leak near the bottom would make a puddle of gas on the ground)
 - A bad fuel-tank pressure sensor because that's how the ECU measures fuel tank leakage...
 
Clear the code (pull fuse #13 in the right-side end of the dashboard) & wait to see if it comes back.
 

I had that a couple years ago.  Tried a new gas cap.  Nothing.  After reading a lot (googled P1456 Accord), the most common fix was the cannister vent shut valve, about $50 online.  It's not a bad fix, but you have to take the cannister off - looks like a small shoe box under the floorpan ahead of the driver's rear wheel.  The only pita about it was the two screws that hold the shut valve to the cannister were rusted in place.  They screw into threaded inserts in the cannister so there's not much you can do if the screws won't come out, other than drill them out and re-tap the holes.

When my CEL came on it too was right after passing emissions, and since the car ran fine I waited almost 2 years to fix it.  It has nothing to do w/ anything except some stupid and meaningless emissions laws.  I religiously check my mileage on every tank, and this 'problem' never affected it at all.

Remember that if you don't clear the CEL somehow like disconnecting the battery, even if you fixed the problem it takes a few drive cycles to clear itself.