definitly need to pull codes to know more , if you can just something to try , remove egr valve and see if its stuck open, that can cause it , but should have thrown the light on , remove cap for fuel filter on engine , see if fuel is getting there , but is almost a waste of time without codes to get started , as far as taking it in, they should reflash it to diagnose it , and you can tell them to make sure they dont and dont have to give them a reason why , just tell them you dont want it reflashed