2004 sienna electric problem

speedometr and heater are not working, OBD code rider gives P0051 HO2S heater control circuit low (bank2 sensor1). Any suggestions how to fix it?

The O2 sensor I can help with. Get a generic O2 sensor from internet (much cheeper) or autoparts store. Make sure it has a heater. Check the number of contacts (wires) on the sensor on your van before you order or purchase. remove the old sensor and cut the wiring harness off about half way down the wires and solder it to your new sensor giving about the same amount of wire length. Use shrink tubing on the wires. The heated O2 sensor costs more than the basic version. If it's really cheep, you probably got the wrong sensor.
Check your fuses on the heater.
No clue on the speedometer. Can you give more info.

I am not sure which one to cut. I am afraid to cut a good one. Can you help me to locate and check it before cutting it?

Bank 2 is the bank in back. The one thats hard to get to of course. Sensor one comes off the exhaust manifold before the two connect. Sensor 2 is after they join together (I think after the catalytic converter).