The connected car has recently evolved from a theoretical concept to reality.Especially in professionally managed fleets, car connectivity promises additional benefits in terms of costs, environment, and maintenance. However, many fleet managers are unaware of using connected car data and still associate telematics with retrofitting each vehicle. Thus, we aim to develop a connected fleet management system to increase fleet operations' efficiency and effectiveness by utilizing multi-brand data from car manufacturers' backend shared by data marketplaces. Thereby, we follow a design science research approach using inputs from the existing body of knowledge and the practical problem domain. Drawing on the theory of effective use, we propose meta-requirements and tentative design principles and instantiate them in a prototype artifact.