To identify the momentary bottleneck of serial production lines with finite buffers is still a challenge in the automobile industry. In literature there are already some detection methods. However, these methods lack the applicability for a real-time fault repair prioritization. A new method is being developed because of this disadvantage to detect the bottlenecks by analyzing the increase and decrease of buffer levels. This method has the benefit of detecting the real-time bottlenecks as well as giving a forecast bottleneck emerging in the near future by indicating the remaining time until a machine becomes one. The new fault repair prioritization method was validated in a material flow simulation of a production line. This simulation indicates a significant output increase. In the following steps, the new method is going to be implemented in a case study.