There are a few different remote types available for the 2004 Sienna, but they all use the same programming type:
http://originalkeyless.com/searchqui...2204+Sienna%22
1. Start with the following conditions: You are in the
drivers seat.
a. Key is out of the ignition
b. Driver door is open (all other doors closed)
c. Driver door is unlocked (other doors don't matter)
2. Insert and remove the key from the ignition twice
within 5 seconds.
3. Close and open the drivers door twice within 40
seconds.
4. Insert the key into the ignition and remove it.
5. Close and open the drivers door twice within 40
seconds.
6. Insert the key into the ignition.
7. Close the door
8. Turn the key in the ignition on and then off.
9. Remove the key from the ignition.
10. The power locks should automatically cycle once to
indicate that you have successfully entered program
mode.
11. Within 40 seconds of the entering program mode.
a. press both transmitter lock and unlock buttons
SIMULTANEOUSLY for a duration of from 1 to 1.5
seconds.
b. within 3 seconds, press the transmitter lock button
for more than 1 second and release.
c. If the transmitter has been sucessfully programmed,
the power locks will automatically cycle once. If they
cycle twice, the remote has not been accepted.
d. If multiple remotes are to be programmed, repeat
steps A-C.
12. Open the driver's door.