I am planning to replace the double-DIN factory headunit on my 2002 Sienna with a single-DIN headunit so that I can install something else. I want to keep using the steering wheel control because it's so convenient, but, after some research, it turned out this can be very tricky on this particular model.
The steering wheel control on the first generation Sienna is not just an analog on-off switches, but a microprocessor that digitally communicates with the headunit using Toyota's AVC-LAN protocol. That's why an aftermarket steering wheel interface, such as SWI-X from PAC Audio does not support Sienna prior to 2003.
Now the fact that I will most unlikely find any aftermarket headunit that can work with the factory steering wheel control leaves me two options.
1) Give up on the factory steering wheel control and instead install a small remote near the steering wheel that can work with an aftermarket stereo.
2) Find a factory/OEM stereo that has just a single-DIN size. I really don't need a tape player that is taking up too much space now. I haven't got any good luck on this yet, either, and my Toyota dealer is very uncooperative on this :-(
If you have any useful info on this, please let me know.