With the increasing popularity of seamless gear changing and smooth driving experience along with the need for high fuel efficiency, transmission system development has rapidly increased in complexity. So too has transmission control software while quality requirements are high and time-to-market is short. As a result, extensive testing and documentation along with quick and efficient development methods are required.FEV responds to these challenges by developing and integrating a transmission software product line with an automated verification and validation process according to the concept of Continuous Integration (CI). Hence, the following paper outlines a software architecture called “PERSIST” where complexity is reduced by a modular architecture approach. Additionally, modularity enables testability and tracking of quality defects to their root cause. To tap this potential, the software is tested, documented and built every night with a high degree of automation in order to uncover quality risks earlier in development.The effect of that approach is shown by examples from a 7-gear series transmission project. Continuous testing and monitoring leads to a steadily increasing quality level while the project plan fulfillment can be tracked on a daily base. It is shown, that the combination of modular architecture and automated verification and validation of software helps improve the overall quality and process in the increasing complexity of the transmission system.