That's about it. Was driving and cel started flashing for a minute and went off. H3 was running fine. Pulled over and put my diagnostic on it and "no codes". I had gotten gas earlier that day so I just reinstalled gas cap just in case. All fluids look ok. Any ideas? Thanks.

 

Without a code it's a mystery.

 

The code could be hiding in the pending codes. Generally a CEL light flashing will set a permanent code. The flashing CEL indicates the problem is happening at that time. It could be a throttle position sensor (or just about anything), but without a code changing it would be pointless. Just a guess in the many systems and inputs/outputs that can cause a CEL flash. Keep us updated, I want to see if my guess is close.