Since the TS 401 does not register sensor id into the ecu, of what effect is the sensor activation which it does? Is it to ensure that the tpms tell-tale  light does not come on? What's the significance of id registration then?

 Well, I think I found it. Yes the TS401 activates the sensors all right and keeps the tpms light off. The significance of id registration is that the tpms ecu is prevented from reading signals from adjacent vehicles. It is restricted from receiving frequencies other than from the sensors in its vehicle and in the specific positions in which the sensors are registered..