Sequoia LTD 2WD with 50,000 miles has VSC Trac, Trac Off, and Engine light on while driving. Used OBD-2 Scanner and gave P0051 H02S Bank 2 Sensor 1 Heater Circuit Low. Has anyone dealt with the problem? Can you tell me how was it fixed and where is this sensor located? By the way how is the VSC related to this error? Thank you!!!!

Did some research on the net and found out the P0051 code relates to the 02 sensor in the exhaust manifold located on the passenger's side. Why the VSC Trac and Trac Off lights also go on might be due to the stering wheel obscuring the engine light for some drivers. Getting back to the sensor, remember it's a sensor and changing it may not fix the problem. Here you can see how to test an O2 sensor: http://auto.howstuffworks.com/framed.htm?parent=question257.htm&url=http://www.forparts.com/o-21.htm
Here you can see description of codes:
http://www.stu-offroad.com/engine/scancodes.htm
And where is the sensor located?
Bank 1 = Left side/drivers side/Cylinders 1-3-5-7
Bank 2 = Right side/passenger side/Cylinders 2-4-6-8
Sensor 1 = Pre-cat
Sensor 2 = After-cat
Before removing parts you might want to check with Toyota since some parts are covered up to 8 years 80,000 miles, which ever comes first.