Each time I have put gas in the car, the check engine light has come on several days later. I have taken it to the dealer each time, and each time they tell me that there was a vacuum leak at the gas cap. They have tested the gas cap and have found no issue with it. However, I find it very difficult to get the gas cap on adequately. The last time I got gas, it took me 7 tries to get the gas cap on straight, but apparently I failed even then as the light came on again today (4 days after I got gas). I have been driving for 40 years and have never had issues with putting the gas cap on after a fill-up. So, either a faulty cap or a bad design. Either way, I am getting tired of having to take the car in to be checked! Thankfully because it is a plug-in hybrid I only fill up every few weeks, but this being the 4th time it has happened I am really starting to get mad!