The logical execution time (LET) programming model has been applied in the automotive industry to master multicore programming of large task systems with complex dependencies. Recent developments in electric powertrains and autonomous vehicle functions raise parallel programming from the multicore level to the vehicle level where the requirements for LET application do not hold any more. This paper introduces System Level LET (SL LET), an extension of LET with relaxed synchronization requirements. While related extensions have been proposed for specific scheduling and communication models before, SL LET can be used with a variety of scheduling algorithms and communication semantics. Furthermore, it can be applied to systems with combinations of LET and other programming models. Yet, SL LET allows end-to-end timing guarantees and preserves essential LET properties required for automotive systems. For illustration, we apply the model to an electric vehicle use case.