RFID technologies are sometimes used into critical domains where the on-line detection of RFID system defects is a must. Moreover, as RFID systems are based on low cost tags which are often used into harsh environment, they do not always ensure robust functioning. This article proposes a new on-line monitoring approach allowing the detection of system defects to enhance system reliability and availability. This approach is based on the characterization of a statistical system parameter - the tag read rate profile - to perform the on-line detection of faulty RFID components. This monitoring approach is compared to classical monitoring approaches for a real case study and through several fault simulations. Results show that the proposed read rate profile monitoring is more efficient than the existing approaches. In addition, results show that this approach should be combined with an existing approach to maximize the fault detection.