The current state of the art for localizing defects in cable systems includes synchronous, multi-channel signal propagation time measurements and the use of time or frequency domain reflectometry. The length of the cable system to be diagnosed limits these technologies. A wave propagating as a result of a dielectric defect is attenuated due to the properties of the transmission path and deformed due to dispersion. The attenuation makes it difficult to detect the signal depending on the background noise level present during the measurement and the distance between the point of origin and the point of measurement. Disadvantages of the current technologies are the high economic and technical effort and the lack of adaptability. Here, a novel approach for a highly sensitive localization of defects in cable systems based on an adaptive cable model is presented. The location of the fault can be determined using the information obtained from the measured signal. First measurements to validate this procedure were carried out and the functionality of the described approach was proven with a minimum localization error of less than 2%. The advantages and disadvantages of the presented approach and its sensitivity are discussed. The sensitivity of the used coupling device allows the detection of a 20 pC pulse injected 6.6 km away.