Photovoltaic (PV) industry has been rapidly grown over the past decades. PV modules are the component of the PV systems that is easily susceptible to rigorous working conditions, which can result in a variety of defects affecting the system’s performance and lifespan if not diagnosed in time. Thus, it is necessary to understand the characterization of each fault and principles of every diagnosis method. This paper provides a comprehensive review of common faults within the context of the PV arrays, addressing the faults type, causes, and their effects on the I-V curve performance. In the previous studies, the main focus of overview is the efficiency and reliability of the direct diagnosis methods. As an important control method, the application of maximum power point tracking (MPPT) has become more and more extensive. This review also presents the latest MPPT-based techniques for diagnosing PV faults. Then techniques for PV diagnosing proposed in recent literature are analyzed and compared to point out their differences, the advantages and limitations and so on. This review will be of more interest to researchers and engineers working on PV power systems.