The growing use of solar photovoltaic systems needs dependable multiport DC-DC converters that can perform at high levels. The performance of converters declines when semiconductor components experience open-circuit or short-circuit faults because these faults require immediate detection to prevent total system failure. A unified system for current control and fault detection based on diode current as a shared state element for output control and fault detection has been developed in this research paper for solar-powered multiport DC-DC converters. The predictive control law establishes duty cycle estimation through charge-second balance principles, which allow voltage regulation to function properly during standard operations without needing extra sensor equipment. The analysis through frequency-domain methods shows the closed-loop system maintains stable operation because it runs with a 1.318 kHz bandwidth and positive phase margin, which allows for quick system response and protection against disturbances. The diagnostic algorithm proposed in this study measures diode current during multiple switching periods to investigate conduction properties, which help identify normal functioning versus OC and SC faults. The experimental tests on a laboratory prototype running at 20 kHz show that the system can detect faults within a time period shorter than one-fourth of the switching cycle, which enables quick fault management and improved system security. The proposed method achieves multiple benefits by lowering both sensor requirements and system processing demands while providing quick fault detection, accurate fault identification, and consistent output control for renewable energy systems and critical power electronic systems. The effectiveness of the proposed method is validated through both simulation and experiment using a 200 W laboratory prototype, where accurate fault detection and control performance are achieved.