p0456 code on a 2001 gcv

I have a 2001 grand cv and I love it.
I am currently getting a p456 code.
I can reset it by disconnecting the battery.
It only comes on in the morning.
If I reset it in the afternoon whon the van is warm its ok.
but the next morning it will flash the code after acouple of minutes
Does any one know what the problem could be or most likely is.
I know it is en emissions error but that is all.
If it is censer related, how much could this thing cost me?

???anyone???

well it was the stipid gas cap AGAIN!
What crap!
I love my van but WTF with these gas caps.
This is the second New gas cap I bought from Chrysler for it.
They need to get their act together on this.
This cap i flipped the seal around and now no engine lite.
I am Really happy that is all it was., But Why would they put crap like that on a van?

How are you getting these codes? Do you have a computer or a little chip that you plug into your car and then check the codes on your pc at home?

I'd like to get one.

Its easy just click you key back and forth on the key swith 2 or three times from off to run and the codes will apear on you odmeter. 2001 or newer.

Well, Heres a little update to my leak.
The engine lite came back on.
It was the 0456 code
So I looked around the filler spout.
Inside , just before the spring door, there was a crack in the black plastic.
I thought Crap! all this time it was a crack.
I took somr crazy glue and sealed it.
It looked like some one shoved the gas nozel in too hard a couple of times.
Since I bought it second hand and I got a good deal on it, I thought WOOOOOHOOO!
Lite is out!
Been out for a month now.
If it happens again, ill replace the filler neck!
Cheers!!