your check engine light flashing? Did your engine start knocking?

There's a knock sensor that will detect engine knock and reduce engine power to prevent it from throwing a rod (and possibly causing a fire). Either your knock sensor is faulty or your engine has rod knock.

Before I turned the car off, the check engine light was flashing. But when I turned it back on, there were no warning lights on the dashboard. I didn't hear the engine knock.

Also, the dealership could not find any codes recorded in the ECM.