Abstract: A vehicle diagnosis system can handle with OBD III as well as OBD II by only adding a transponder to an OBD II system. The vehicle diagnosis system includes an engine ECU for controlling an engine device such as injector and storing a diagnosis data, a K-line connected to the engine ECU, a transponder connected to the K-line, and a connector connected to the K-line for detachably connecting an external scan tool that reads the diagnosis data stored in the engine ECU. The transponder receives a request from a receiver system by radio, reads the diagnosis based on the request, and sends the read diagnosis data to the receiver system.