2004 sienna electric problem

1 How to locate speed sensor?
2 How to fix heater control valve? only cold air is blowing in

For the speedometer: There is usually a cable that connects the trans to the speedometer. At the end of the cable that goes into the trans is a gear. Frequently, the gear isn't pushed all the way in and doesn't mesh with the gear in the trans. I haven't looked at my sienna yet, but the end usually slips into the trans and has a clip that bolts on to hold the cable in.
Heater: I'd bet the cable that goes between the control panel and heater box (? - it's what I call it) has come loose or the arm that it connects to has broken. You have to go into the dash to work on this. Get a Haynes or chiltons service manual from an autoparts store before you try. The instrument panel cover has three hidden screws on the bottom - be careful to remove them or you will break the panel. The panel will cost you $170 or so if you break it.
You can ask the dealer that you bought your van from for the service manual that you were asking about in your other thread. They probably won't give it to you, but you can ask. The toyota service manuals usually run about ~$110, but they are worth it. I always buy one when I get a new car.