The present invention such as active diagnostic algorithms is developed not only to realize the early detection of degraded vacuum pumps for the protection of pump failure but also to provide their predictive maintenance. According to the present invention, it is possible to find simple and effective ways to deal with technical problems arising from the large variability of the pump-by-pump operation characteristics and the multiple process conditions where pumps run under the idle operation and gas-loaded operation conditions alternately, especially in semiconductor manufacturing process.