2000 Caravan P0401 code

Hi

we just bought a 2000 caravan and check engine light came on so we took it to checkers. Found out the code is P0401. After doing research on net found out there could be few reasons for that code. The engine runs fine. What should be the next step in determining if it's ERG valve or DPFE sensor or vacuum leak? Where are these components located on van? What is the least expensive and most common solution?

Thanks