02' T&C warning light/ emissions problem

I have a check engine light that has been on for a couple of months. I took it to a mechanic that i know well and trust. He pulled the code and said that it was an "emissions" problem. He cleared the light and told me to get a new gas cap. I went to the Chrysler dealership and put the new $18 cap on the van. Within 3 days it came back on. He assure me that it was not a danger and we drove it on a vacation trip of 2000 miles. When i got back he looked it over and said he replaced a couple of vacuum hoses and thought that would fix it. 3-4 days later it came back on again. He looked it all over and said he could not find it. He said I could take it to a dealer with the proper equipment they would pump smoke in the lines and look for it? Any suggestions out there of something to look for?
Thanks!

Having the evap smoked for leaks is a good start. There are a couple of evap hoses that are real common to crack and leak but your guy should have spotted them.

Thanks for the advice. I hope he replaced the hoses you are talking about? He said he replaced "a couple" of hoses he thought looked like they might fail? How much is it gonna run to have it smoked out? Do you think it's worth messing with? What is it going to hurt if i ignore it? Is it only effect the gas mileage or what?

Thanks...

Had the same problem replaced 2 small vacuum hoses on passenger side of engine compartment they are about 2-3 inches long and have a valve connection between them. This is where the connect smoke machine to evap system. They looked fine until you look underneath and they were split completely