2006 Dodge Caravan engine code 406

My engine light came on and after a couple of days my car would not start. It had been running fine.
i had the van jump started and it ran fine for a few more days then it stopped when I parked at a store.I tried jumping it again but to no avail. Alll my lights and horn radio etc still worked. So I didnt think it was the battery, but I replaced it anyway since it was about 3 yrs old and still not starting. No clicking noise or anything. So I had it towed home the next day and on the way we stopped by auto zone and they told me it was code number 406 egr valve. What does it mean and will that cause the car to completely stop running as it has now done? Is this hard to replace? I havent worked on cars for a number of yrs and not really sure where to look for this. Any help would be great