OBD system development matures throughout the phases of vehicle program. Ensuring a robust implementation of OBD system is critical to meeting the regulatory requirements and avoiding customer dissatisfaction. Therefore, it is crucial to demand comprehensive testing of the system that captures all potential events. In this paper, we outline a methodology for evaluating the maturity of the OBD system throughout the development process. Determining critical monitors and establishing solid targets for performance of each monitor is the initial stage of the process. Measuring the maturity of the system by utilizing reliability growth models is demonstrated in this paper. The results of this assessment are used for evaluating the readiness of the system prior to launch.