Bias on ground wire: o2 sensor

I am confused how there can be a bias voltage on a ground wire. It seems it would just get pulled to ground all the time. The only way that I can see it is if there was a transistor on the ground wire that would allow/block current flow like on an output with a bias. See picture.

Chrysler vehicle ?
A normal 0.1 to 0.9v O2 sensor is really a sensor in the normal way of thinking it is fuel cell --- it generates a voltage so if the ground is floating at some bias voltage above 0v the 0.1 to 0.9v will add to this bias voltage.

I understand voltage being on the ground wire in a floating ground situation. But if you unplug the sensor and there is still a bias on the ground, it could not be from a floating ground. And Paul Danner said that sometimes there is a bias ONLY on the ground wire. This is the situation that confuses me.

It isn't a floating ground probably best to describe it as an elevated ground.
The sensor dosen't care what voltage it grounds it at it simply adds to the voltage, think of it as two batteries in series.

Floating crank sensors are a bit different the ecu treats those as a AC signal.

Yes. The dc voltage elevates the ac voltage. The ac "rides" on top of dc voltage that is produced by the sensor. But to have voltage on a ground wire UNPLUGGED would require a positive voltage coming from the computer on the ground wire. Unplugged implies that voltage from the computer on the (+) wire could not be on the ground wire. It also implies that there would be no sensor voltage because it is unplugged. So how can there be a positive bias voltage on the ground wire unplugged?

Could this be right?

Where is this "AC" voltage coming from? It's all DC.

Consider a two D cell batteries connected in series like you'd find in a flashlight. What's the voltage testing from the two ends?

Now place a voltmeters negative lead in between the two cells and the positive lead on the seconds cell positive. Now imagine that the second battery fluctuates in voltage. What does your meter read?

Part of the problem here is the nebulous and changing way the term "bias" is used to describe automotive circuits.

Flatrater:

Not being sarcastic, just looking to learn.

What do you mean by “it’s all DC”?

Even a variable reluctance sensor?