Abstract: Protective circuit and a method for operating said protective circuit in particular for overvoltage protection for an electronic control system for a motor vehicle protective circuit, comprising a control unit (1) and a switch unit, with the switch unit monitoring an input voltage of a voltage regulator (2), which is directly or indirectly associated with the supply voltage (VCC) of the control unit (1). If this input voltage (UBAT) exceeds a predetermined threshold voltage (USCHWELLE), the control unit (1) switches in one or more loads. If the control unit has an idle mode and an operating mode, it is switched from idle mode to operating mode and if necessary a further load (RL) is switched in.

Abstract: The invention relates to a request signal that is transmitted between a first and an additional transmitting and receiving device by means of a bi-directional first communications path. According to said request signal, a second communications path is established for a predetermined time interval and the receiving power in the additional transmitting and receiving device is measured by means of a measuring device.