The narow band O2 is essentially that, it has a very narrow band of which it reads accurately. In fact, that range is so small it'* almost just a switch and can essentially be thought of that way. While not getting into detail about the inner workings of engine management systems, the narrow band O2 essentially tells the ECU either to add fuel or take away fuel depending on which side of the switch it'* on. Just where does that switch point happen to be, well, it'* at the 14.7:1 as mentioned above. While this does a good job of telling you if your car is running rich or lean, it doesn't accurately tell you how rich or how lean.

This is where the wideband O2 steps into the picture. It has a broad range of measurement and can accurately tell you where you are sitting air-fuel wise. Why is this such a good thing, well, in order for a car to make good, safe power you want to run it a little on the rich side of things. For example a typical turbo car will operate best running at an air-fuel ratio of approximately 12.3:1. On the narrowband O2 you'd have a hard time finding this point, but with use of a wideband O2 you can accurately read where you are. It'* the best way to get air-fuel ratios sorted out and you'd be surprised at the difference in power a properly tuned motor will have.