Diagnostic system for a motor vehicle

Claim 1

A diagnostic system for diagnosing an electronic control system which controls an engine mounted on a motor vehicle, said electronic control system having sensing means for detecting operating conditions of said engine and first memory means for storing data from said sensing means, said diagnostic system comprising: a diagnostic device comprising a display for displaying diagnosis data, a control unit for controlling the operations of said diagnosis device, a keyboard for inputting signals into said control unit of said diagnostic device, and connecting means for connecting said diagnostic device with said electronic control system; second memory means provided in said control unit of said diagnostic device for storing first programs provided to perform a particular diagnosis with respect to said electronic control system; third memory means being provided in said electronic control system for storing second programs to diagnosis said electronic control system in which said third memory means is provided and to control the engine respectively; designating means responsive to input signals of said keyboard for selectively designating the electronic control system or the diagnostic device either as a master or a slave to provide master mode or slave mode; and wherein when said electronic control system is designated in the master mode and the diagnostic device is designated in the slave mode, the diagnosis of said electronic control system is performed by said second programs, and when said electronic control system is designated in the slave mode and the diagnostic device is designated in the master mode, the diagnosis of said electronic control system is performed by said first programs.