This paper presents a remote diagnostic system for vehicles via the use of On-Board Diagnostic (OBD), APP, and remote monitoring software techniques. Recently, the close loops of internet increase the communication safety, but also increase the cost and the lack of convenience.The main parts of the proposed system are vehicle on-board computer, the APP of a smartphone, and the free monitoring software of team viewer. First, the OBD Interpreter IC can obtain the vehicle's status and from the ELM electronics respectively. Then the smartphone will connect with OBD adapter from the vehicle's Data Link Connector through Bluetooth network to transmit the real-time vehicle system status and location of the user. Finally, the smartphone could show the remote vehicle's status including data graphing, information data list, engine rpm, engine calculated load ratio, engine coolant temperature, and diagnostic trouble codes. According to the experimental results, the proposed system can help vehicle service technician and car driver to understand the fault conditions of the remote vehicle and can decrease the vehicle's rescue cost. Therefore this system can increase the efficient of repair performance and decrease the vehicle's air pollution due to the technician and vehicle driver who find the diagnostic trouble messages in time.