Egr

I have "service engine soon" the code (from autozone) is EGR. They say it is either the EGR Valve, Switch or one other possibility in the EGR system he mentioned, but I have forgotten. They have no parts avail for it, so they suggested a dealer. Anyone have any troubleshooting experience with this? I plan to pour over my Haynes tonight, but any assitance on norrowing down culprit would be appreciated

almost forgot...99 Grand Voyager 3.3L flexfuel engine