A method for detecting a malfunction or defect of a sensor of a vehicle safety device uses a control unit of the vehicle safety device and at least one self-testing sensor which is separate from the control unit and transmits measuring values to the control unit. The following steps are performed: a) The sensor performs the self-test of the sensor, wherein the measuring section of the sensor is activated in a simulated manner in order to generate a test measuring value in response to the simulated activation, b) a signal is transmitted to the control unit which includes at least one of: a ratio of test measuring value to intensity of the simulated activation, a deviation of the test measuring value from the simulated activation and a test measuring value, c) it is checked by means of the control unit whether at least one of the ratio, the deviation and the measuring value is plausible, d) the control unit determines that the sensor has malfunctioned or is defective if at least one on the ratio, the deviation and the test measuring value is considered to be non-plausible.