Up stream o2 Oxygen sensor above 3 volts?

[CTScott]

Originally Posted by Yangs

I test and replace o2 sensor before on other cars but this time with my Yaris I have a very bizarre situation. While the car is fully warm in operation temperature According to my multimeter, it show's little above 3.00 volts and it doesn't fluctuate from 0 volt to 3.00..."a steady voltage" I try to give it some gas but it still doesn't fluctuate. What's very strange is that the instrument cluster does NOT throw any trouble code and even thou I stick in a diagnostic scan tool it doesn't show any trouble code and emission status are good. Not to mention MY GAS MILEAGE WENT GARBAGE!!! I never heard 3 volts before on a o2 sensor. Maybe Toyota did some thing different from other car manufactures or maybe I have a bad o2 or a short some where?

Also the down stream o2 sensor read 0 volts at idle.

With the sensors used on the Yaris the voltage is kept constant and the ECM measures the current required to maintain the voltage, so you can not use a volt meter to troubleshoot them other than seeing if they are completely dead.