1. Get in the car, close the door. Perform steps 2-6 fairly quickly (less than 3 sec's total time). (The key should not return to the OFF position through this next sequence!)
2. Turn key to 'ON' position 3. then back to 'ACC' 4. then to 'ON' 5. then back to 'ACC' 6. then to 'ON'
It was a loose gas cap (durr) code P0455...no worries !
I thought it would be like when it shows you what tire is low. That comes up when you start the car. Guess not, hopefully my CEL light won't come on so I'll never know.