A method for supplying vacuum for a pneumatic brake booster for a motor vehicle braking system, using an electromotively-driven displacement type pump assembly. At least one pressure sensor for monitoring a pneumatic pressure is associated with the pump assembly, and electric signals of the pressure sensor are fed to an electronic unit, analyzed, and processed in order to regulate the pressure. A plausibility check of the pressure sensor signal is carried out by a pressure value amplitude being determined, by signal analysis, in the form of a difference between a maximum pressure value and a minimum pressure value within a stroke of the displacement element, and this being compared to a stored comparison value wherein if the pressure value amplitude deviates from the comparison value by a defined amount, the signal of the pressure sensor is then defined as implausible.