Functional dependencies and feature interactions in automotive software systems are a major source of erroneous and deficient behavior. To overcome these problems, many approaches exist that focus on modeling these functional dependencies in early stages of system design. However, there are only few empirical studies that report on the extent of such dependencies in industrial software systems and how they are considered in an industrial development context. In this paper, we analyze the functional architecture of a real automotive software system with the aim to assess the extent, awareness and importance of interactions between features of a future vehicle. Our results show that within the functional architecture at least 85% of the analyzed vehicle features depend on each other. They furthermore show that the developers are not aware of a large number of these dependencies when they are modeled solely on an architectural level. Therefore, the developers mention the need for a more precise specification of feature interactions, e.g., for the execution of comprehensive impact analyses. These results challenge the current development methods and emphasize the need for an extensive modeling of features and their dependencies in requirements engineering.