A flashing CEL indicates an issue that can cause damage to the engine or emissions, most commonly it's for misfires (which can also cause a vibration while it's happening). Not sure what you're using, but it might be worth your time to try something different to check for codes, preferably a scanner.
The explanation still stands, a flashing CEL typically indicates a misfire. Not sure why no code is getting stored. If it's possible to replicate the problem easily, I'd suggest try taking somebody from the service department along to demonstrate the issue.
you hit the nail on the head. cylinder #5 was misfiring which caused the valve to freeze and damage the cam shaft. funny thing is i brought it back for a tricking sounds 1 month after i had it and the dealership said they didn't find anything. but it's all fixed and we are back off the road.