Abstract: A power supply system for a vehicle has at least one control unit with two power supply terminals that are each protected against overload by a fuse. The first power supply terminal is connected to a voltage regulator for the microcomputer of the control unit and to the accumulator via the quiescent current switch, while the second power supply terminal is connected to the accumulator via a fuse. The first power supply terminal supplies the microcomputer with energy, while the second power supply terminal actuates one power switch per control unit in order to supply energy to the output stages of an actuator which is operated by the control unit. The on-board vehicle power system control unit activates the quiescent current switch in order to deactivate the microcomputer, while the power switches of the same control unit are supplied with power.

Abstract: A method for checking lead defects in a two-wire bus system compares the voltage levels on the two wires with certain threshold values, with the comparison being made with the threshold values in the dominant and recessive states. A circuit for performing the method has one input of a first comparator connected with one wire, an input of a second comparator connected with the other wire, and the other inputs of the first and second comparators each being subjected to a voltage that is between the two voltage values on the wires in the dominant and recessive states in normal operation. One input of a third comparator also is connected with one wire, and one input of a fourth comparator is connected with the other wire, with the other inputs of the third and fourth comparators each being subjected to a voltage that is above the maximum voltage value on the wires in the dominant and recessive states during normal operation.

Abstract: A method for pinpointing a short circuit or cable break in a two-wire bus system has the two-wire bus system being subjected at at least one point to a pulse of such a steepness that a reflection occurs at the location of the short circuit and/or cable break. The short circuit or cable break is pinpointed on the basis of the propagation time of the pulse. A circuit includes a pulse generator connected with a gate chain with a shift register, so that the passage of the signal through the gate chain is launched when a pulse is injected into the two-wire bus system. The distance of the short circuit or cable break from the point at which the pulse generator is connected to the two-wire bus system is determined from the number of gates traversed. In addition, a method for pinpointing a cable break, determines that a cable break in the connecting leads of a subscriber has occurred if this subscriber cannot be reached by communication over the bus.