Got a check engine light out of the blue. The car's diagnosis didn't know what it was so took it in to the dealer.

They said that it was caused by "overfilling" the gas reservoir for the extender that then saturated the fuel assembly and would require a $2,000 repair. Despite the fact that the check engine light came on over a month from the last time gas was put in, and that there is NO WAY to overfill a gas tank unless you continue to press the nozzle after it goes off, the dealer (Century West BMW in Los Angeles) refused to do anything about it. BMW also refused to do ANYTHING about it. They said I magically should have known how much gas to put in. I replied that the ONLY way to know if it's full is when the pump goes off.

This appears to be an issue referenced in several blogs but BMW claims that it is not significant. They said there was no one higher I could complain to.

So, its a significant ($2,000) issue and the owner has no control over it. Good luck when putting gas in the REX. I guess best advice is to just put a little in and hope it's not full.