Automotive cyber-physical systems are energy-aware and safety-critical systems where energy consumption should be controlled from a perspective of design constraints and reliability should be enhanced toward functional safety goal assurance. In this paper, we solve the problem of reliability enhancement of an automotive function (i.e., functionality or application) under energy and response-time constraints based on the dynamic voltage and frequency scaling technique. The problem is solved by a two-stage solution, namely, response-time reduction under energy constraint and reliability enhancement under energy and response-time constraints. The first stage is solved by proposing average energy preallocation, and the second stage is solved by proposing a reliability-enhancement technique based on the first stage. Examples and experiments show that the proposed solution can not only assure energy and response-time constraints, but also enhances reliability as much as 16.66% compared with its counterpart.