2003 Toyota Corolla Diesel gas in unleaded car

I accidentally put about 4 gallons of deisel in my unleaded car. There was probably about a gallon of unleaded in the tank. I drove about a mile to work but at lunch the car wouldn't start. It was towed to the garage where they tested it and found it was the deisel gas. They emptied the fuel tank, refilled it with unleaded and flushed the system with the unleaded. The car is running fine but the check engine light has come on (about three days later). What should I do? Is there permanent damage to the engine?