We had a similar situation on a 2003 Corolla at 32,000 miles.  Light came
on, and I went to the Toyota dealer.  They put their computer code reader on
it and when they did, the light went out, and no codes were listed.  They
said it happens, and that if it is a major malfunction (loss of oil
pressure, overheating, etc...), the code will remain in your computer until
it is fixed.  They also said that starting and stopping the engine several
times will usually clear a minor code.  No charge for the check, and the
light has remained out.  The only thing I think might have caused it to come
on was water sprayed on the car the night before and it may have gotten into
the engine compartment causing the check engine light to come on.

Your car is OBD II (On Board Diagnostics, Level 2) compliant. There is NO
REASON for the dealership to keep you car all day, then bring it to the
front without doing anything more than scratch their head.

If you look along the bottom edge of the dash board in the area where your
left leg rests while you drive, you will find a connector. (You might find a
cover with OBD II or a variant molded on it.) This connector is where you
would connect the code reader. It is so easy that the Service Writer of any
dealership should provide the service for free when you pull into the
driveway. The Service Writer can pull the codes in less than a minute, and
tell you precisely what the expected service activity will be. Any dealer
that charges for pulling codes should be charged with highway robbery, but
that's just me I suppose.

The code reader will spit out a code like P0440, and the Service Writer
should tell you, "Mrs. Jones, the code reader says the framis valve is
complaining. We'll be looking at the framis valve and its wiring to see
where the trouble is." Then he should write on the service ticket, P0440,
Framis Valve. If there are other codes, then they will all come up at the
same time. More often than not multiple codes are all variants on the same
code. Fix the root and the other codes will be fixed at the same time.

If you wanted to drive down to an AutoZone store, they will let you pull
codes with their code reader for free. They (I think) are prohibited from
pulling codes for you because they are taking food out of the mouths of
service centers that charge for the service. But the service providers can
not prevent you from pulling your own codes and then affecting the repairs.
I understand that you might not be able to affect the repairs, but you can
pull the codes and know something about what is wrong with your car before
you take it in.

PS
P0440 is a malfunction of the Evaporative Emissions Control System, and most
often this is a fault that is rooted in the gas cap. I should have picked a
different fictitious code. Sorry.