Abstract: A computer based technician terminal is connected to a vehicle being serviced using an assembly line data link (ALDL) connection from an on-board computer. The data link provides status information and fault codes. The technician is led through various procedures. During set up, the technician connects an ALDL cable from the terminal to the vehicle, the vehicle indentification number (VIN) is entered and vehicle options are identified. A fault detection procedure (FDP) in the terminal detects vehicle malfunctions by interrogating data received (via the ALDL) from the on-board computer. A fault analysis procedure (FAP), using the fault codes from a table as arguments, does a sequential compare against the contents of a fault analysis table containing fault codes. In a fault sequencing procedure (FSP), for each fault code passed by the FAP, there is a list containing the name(s) of one or more isolation procedures.