RFID systems are complex heterogeneous systems, consisting of analog and digital hardware components and software components. RFID technologies are often used into critical domains or within harsh environments. But as RFID systems are only based on low cost and low-performance equipments, they do not always ensure robust communications. All these points make the on-line testing of RFID systems a very complex task. This article proposes a new on-line testing approach allowing the detection of tags defects to enhance system reliability and availability. This approach is based on the characterization of a statistical system parameter, the tag Read-Error-Rate, to perform the on-line detection of faulty RFID components. As an introduction to RFID tags on-line testing, a Failure Modes and Effects Analysis first describes the effects of the potential defects on these systems. Second, a SystemC model of the RFID system is proposed as a way to evaluate the proposed test solutions. Then, our solution to enhance system reliability is presented. Finally, validation of our on-line test approach using system-level simulation is discussed.