I would (obviously) like to suggest water got into somewhere electrical it shouldn't have. Check the TCU and ECU in the box behind the RH headlight. If water got in here it could cause a short or a TCU communication issue which may explain the no codes. What are you using to test for the codes by t...

Magic arrow showed up after a engine bay wash (I know, I know). Thought it was a fluke, code reader said P0172 (turbo boost elbow) cleared code. Drove for 3 blocks, flashing arrow/CEL returns. Haven't been able to complete "drive cycles" after clearing initial codes, due to trans in 3rd ge...