Feedback Closed & Open Loop

In open loop mode, the engine does its own thing and “don’t listen to nobody”, it just runs off a set of instructions based on where the throttle is at, where the revs are, and so on.

The sensor that feeds back for closed loop mode in question is a lambda sensor, also known as an oxygen sensor or air/fuel ratio mixture sensor. In closed loop mode, the engine listens to the lambda sensor to adjust fuel/air mixture. In open loop mode, it doesn’t!