This paper presents a novel Hardware-in-the-Loop (HiL) testing framework for validating panoramic Sunroof systems independent of infotainment module availability. The increasing complexity of modern automotive features—such as rain-sensing auto-close, global closure, and voice-command operation—has rendered traditional vehicle-based validation methods inefficient, resource-intensive, and late in the development cycle. To overcome these challenges, a real-time HiL system was developed using the Real time simulation, integrated with Simulink-based models for simulation, control, and fault injection. Unlike prior approaches that depend on complete vehicle integration, this methodology enables early-stage testing of Sunroof ECU behavior across open, close, tilt, and shade operations, even under multi-source input conflicts and fault conditions. Key innovations include the emulation of real-world conditions such as simultaneous voice and manual commands, sensor faults, and environmental triggers using a software-controlled test environment. The system helps more than 60 automated test cases and makes regression testing easier without hardware reconfiguration, accelerating feedback cycles and enhancing software readiness. The results show that the framework efficiently identifies test case failures and speeds up validation timelines. The simulation model allows reuse for all ECU variants and streamlines test expansion for future functionalities. Simulation contributes a scalable and infotainment-free testing approach that enhances product quality, reduces dependency on physical prototypes, and supports continuous system integration in automotive control system.