System and process for the determination of the position of at least a rotating part by use of a position signal

The system has a synchronization unit (7) coupled to a sensor (6) and a detection device (4), and including a determination device to determine an activation position of the device (4) when a transponder (3) is in transmission/reception cone of communication of the device (4). An activation device activates the device (4) to measure vehicle parameter e.g. tire pressure, by comparing a position of a coder with the activation position. Independent claims are also included for the following: (A) a process of determining a parameter of a rotating unit with respect to a frame (B) a motor vehicle including a system for determining a parameter of a rotation unit of a vehicle.