In communication systems, electrical connectors could easily be subjected to contaminants in the atmospheric environments.The presence of the contaminants could lead to connector failure which is one of the major causes of low communication quality.In this work, signal characteristics of faulty connectors in communication systems were analyzed in order to detect and locate the faulty connectors accurately and rapidly.The results show that the amplifier circuit and mixer circuit can be the typical circuit modules for the fault diagnosis of the connectors in a communication system.A method of connector fault detection based on the norm of MMSE (minimum mean square error) is proposed.