When the computer receives a rich signal (high voltage) from the O2 sensor, it leans the fuel mixture to reduce the sensor's reading. When the O2 sensor reading goes lean (low voltage), the computer reverses again making the fuel mixture go rich.
Chemistry and physics are branches of science that both study matter. The difference between the two lies in their scope and approach. Chemists and physicists are trained differently, and they have different professional roles, even when working in a team.
Well, this is another example of a nonexistent debate between Chemistry and Physics. I only found chemists talking about it and not a single physicist really devoting any time to it. Chemistry is an empirical practice rather than a deductive science. On the other hand, physics is a deductive discipline rather than an empirical one. Here is an illustration of my point. Take for instance the 1996 Nobel Prize in Chemistry awarded to three chemists for their discovery of fullerenes.