I had the fuel filler flap on my Rex pop open today while driving. It was quite a distance before I was able to stop and close it. I have no idea why it popped open. By the time I was able to stop, the check engine light came on.
I have never used the range extender except for a test a month or so ago, so it had to be caused by the open flap.
I only drove a short distance after getting out and closing the flap, so I don't know whether it might have self-reset had I driven further. I'll see whether I can reset it through the service port. Otherwise, I'll stop by the dealer and have it reset. I hate that thing being on even tho it is meaningless.