On-Board Diagnostics (OBD) system is developed to detect vehicle system error and malfunction for health diagnosis. OBD generates warning signals to vehicle operators as well as the maintenance engineers. However, once a warning signal is being generated, most operators are not knowledgeable to take any action on it. Data acquisition has to rely on maintenance engineer using special tools. Based on such a practical demand, this paper presents a new vehicle on-line diagnosis and real time early warning system to acquire OBD signals and transmit to a Server of Maintenance Center via GPRS mobile communication for immediate actions. In this paper, hardware and software in both design and implementation are discussed with preliminary tests. The test functions of the proposed system fulfill the rising requirements for modern vehicle system.