Oxygen Sessor

I am not 100 % sure but I believe it is A rich mixture will produce almost 900 millivolts. A lean mixture produces about 100 millivolts or less. The sensor does not produce in-between voltages with any regularity. Sorry I am not certain on the exact number hope this helps some.

Sorry to be posting again but as I read a little more I found a bit more info.

When the engine has more fuel than needed, all
available Oxygen is consumed in the cylinder and gasses leaving
through the exhaust contain almost no Oxygen. This sends out a
voltage greater than 0.45 volts. If the engine is running lean,
all fuel is burned, and the extra Oxygen leaves the cylinder and
flows into the exhaust. In this case, the sensor voltage goes
lower than 0.45 volts. Usually the output range seen seen is
0.2 to 0.7 volts.

Not including the original sensor this would be the 2nd one put into the car. I returned the first replacement thinking is may be NG. The new unit is reading a steady 440 mv. Is there any way to test the oxygen sensor out of the vehicle.

Thank you

You can test the O2 sensor out of the engine, and I tried it, but could never get it to work.
I"ve read that you should clamp the sensor down and use a voltometer. Positive to the sensor wire, and ground to the base (bolt area) of the sensor. Use a propane torch, and heat the tip of the sensor untill it turns red, making sure that the heat is blowing inside the sensor. You should get a reading on the voltometer that it's producing a voltage.
If so, when you move the sensor in and out of the flame, the meter rating should change slightly. If not, it's probably bad. If it does, it's probably working.
In my case, I couldn't get a brand new sensor that works in my car, to do "anything" with this test. So. Who knows.