The black carbon on the sensor in the picture is normal. That is from the exhaust system. I'm not sure what was read, but if there was something like engine coolant getting into the system, that could cause the sensor to have a whitish color. Also, if the engine was running extremely lean (too much air/ not enough fuel) it would look very clean. If the engine was burning an excessive amount of oil, the entire thing would be black. I suspect that was what was meant.
As far as yours. chances are it just wore out and went bad internally.
Here are two links you may find of interest. The first discusses what the sensor is, how it works, and its purpose. The second explains how to test one.
I hope this helps answer your question, which is a good one.
Let me know.
Friday, August 20th, 2021 AT 10:09 PM