Check engine light turns on, transmission not shifting properly, speed sensor location needed

Check light comes on when driving, at high speeds the rev goes up and it's not changing past fourth gear apparently. Computer diagnostics says rear speed sensor little or no current. Where is this sensor located on a 2007 Toyota fielder s 2zr engine?

Whenever the check light appears the engine runs at high RPMs and no fuel economy. When I stop, switch off the engine and restart it the check light is gone but when I drive off it reappears after a short while. And transmission shifts abnormally.