In today's fast-challenging business environment, automobile manufacturers are required to supply customers with high-quality vehicles at competitive prices. However, existing research on factors influencing service quality lacks a detailed and systematic understanding, and there is no consensus study on causal relationship and measuring the weights of service quality factors in the automotive manufacturing industry. This study provides an integrated technique for evaluating the automotive service quality in the context of VinFast-the Vietnamese leading brand. First, the Grey Theory System (GTS) is utilized to estimate the subjective views of the decision maker (DM) and overcome incomplete and vague decision information. Then, a Decision-Making Trial and Evaluation Laboratory approach integrated with GTS (Grey-DEMATEL) is proposed not only to define the cause-effect factors but also to quantify the causal relationship of proposed criteria, which is based on comprehensive analyses of the current service quality literature and experts' opinions, as well as to capture the criteria weights. The results show that the weights of main criteria can be sorted as follow: Tangibility > Reliability > Assurance > Pricing > Empathy > Responsiveness. Among the proposed sub-criteria, Pricing is the top concern compared to other dimensions, making it a prerequisite for VinFast. The causal relationships of VinFast's service quality are discovered by the Grey-DEMATEL technique. The findings also indicated a rising need for VinFast to focus on Empathy. Furthermore, the proposed model might be used as a decision support tool to contribute to the literature on service quality, provide recommendations for future study, and assist managers in improving service quality more efficiently.