I re-post my experience agin to share with, but may not work in your situation!
I have a 2001 Sienna, which has the same problem. Check the code at AutoZone indicates that O2 sensor may have problem, I did the following work by myself to turn that light off:
1) clean the O2 sensor with soft tissue;
2) disconnect the battary, then re-connect;
3) driving for more than 100 miles;
4) if the light is not on, go to the inspect!
If you go to the shop, they may charge $ 80-100 for diagnosis, then to solve the problem. I have 1996 Camry had the same problem, I went to the dealer, they checked for $80, then simply tight the gas tank cap, the light went off. I don't know why Japanese cars are more likely to have this kind of problems. Hope this could help you a little bit!