Everything went perfect until I drove off the lot....

Everything went perfect until I drove off the lot. I live in Ri so I drove up there for a used Transit 250. On my way home in border with Ri the light went on, and it's still on. It's to far to drive and service it to the dealer. And they don't have a dealer that they work with in Ri.
I want go out of state again to purchase a car no meter how good the deal is for these type of reasons.
I have a hard time believing that they did like they say 200 plus inspection point and 30 minutes drive something goes wrong.