In the high competition, the service time is one of many important factors that some customers are likely to concern. This thesis would like to investigate the root causes of the unnecessary activities in a selected authorised service centre which can be improved overall service lead time especially engine oil changing service and light commercial vehicles only (Pick-up and SUV) and to be a prototype improvement plan to suggest other authorised service centres in Thailand in the future. The procedure of engine oil change service can be grouped into 3 phases including the pre-checking, maintenance and post-checking phase. The idea of lean, some lean strategies and the analysis of the external and internal environments, for example, Value Stream Mapping, Non-value activities (Muda), The continuous improvement (KAIZEN), ECRS method, Five-Forces model, SWOT analysis and Fishbone diagram are utilised for finding issues and wasteful exercises inside the current process. Furthermore, the service centre can utilise the concept of Dual mechanics to make servicing time reduce by half in the maintenance phase. Overall, the inefficiency wasteful factors can be divided into 3 major groups namely the issue of inefficiency of service advisor (SA), the issue of poor workshop management and the issue of parts management and the total number of non-value activities is 10 sub-points. So, this research will give recommendations and compare the result between before and after and future improving the engine oil change process. All related issues will decrease which can enhance the faster service time of engine oil changing to compete within the after-sales car business.