When do you have to service transmission on 2004 Toyota Sienna?

Transmission on Toyota Sienna, does not need servicing. Toyota made the trans service free by using special synthetic trans oil called T-IV. That oil is a non-petroleom oil, and should not be mix with other reg trans oil. But if you like to freshen up the T-IV synthetic oil, you will need a 10MM hex key for the side plug on the transmission, there is will come out about 4 quarts, when removing the plug. The trans oil filter is a wire mesh type and does not need to be replaced. again if you like you can change or clean. parts cost from 22.00 to 60.00 dollars above items can be found here on the internet very cheap.