in response to some of the replies stating that they thought it was the type of system that compares wheel revolutions for readings. that is not the case with the nissan sensors. the sensors are actually pressure sensor units on the valve stem, not the cheaper tire system like the ABS one mentioned. I had the dealer confirm this with a manual and a dealer hand out. the bad thing about the ABS versions aside from just cutting cost corners for manufacturers is that in a long corner the wheels rotate at different speeds. thus the one side of tires may seem smaller since the inner side makes more revolutions. thus the computer thinks flats are in the works and flags it. and thus pissing owners off and making them rather not have it in the first place. hope that helps people.