Toyota Repair: Check Engine & VSC indicators, charcoal filter, gas tank

Question
I took my 2006 Avalon to the dealer today because both the "check engine" and "VSC" indicators lit up over the weekend and wouldn't go off.  Surprise!  They're replacing the gas tank and the charcoal filter.  I'm very confused.  How do those two items cause two different lights, one of which I would think would have something to do with the anti-locks?  Are they addressing one problem and ignoring another?

Answer
I'm sorry. I can't really comment on the problem, as you haven't told me anything about it. You can't just tell someone "the lights are on". OBD-II standards monitor hundreds of data sets. (Right now about 650-800 specific critea on that car can store a code on the sub-systems.)

You should have had the codes scanned so you know what they are. Always do that. Many places will do it for free. Autozone for one.