The cause of the trouble light I posted about last week turned out to be a faulty seal on the gas cap. That is, the cap was not tightly fastened or had somehow come loose since I last filled up. This caused a vacuum leak (a misnomer if ever there was one–vacuum is not leaking out, air is leaking in!) in the vapor return line, which is apparently serious enough that the “get ye to the dealership” light comes on.

So I feel slightly foolish. On the other hand, it was time for 3,000 mile service as well as 85K service, so we took care of that at the same time.