the esp module looks at all the wheelspeeds and determines the true speed, then sends it over can to the cluster/m.e. and whatever else wants to know. This is how some of the benz's can determine if a tire has low pressure it notices when the car is going straight one of the tires has a significantly higher rpm due to smaller diameter of a tire low on air. This is before they were using tpc. it also uses that same logic and looks at your steering angle sensor and if it sees a certain steering angle say 10 degrees off and notices all the wheels have identical speeds it will throw a esp code- so you have to get an alignment done.