Today's automotive service technicians use on-board diagnostics (OBD) as the primary diagnostic tool in diagnosing faults in computerized vehicle systems. However, owing to the inherent limitations of the system architecture of OBD, the scope and accuracy of the diagnostic information available from it is frequently insufficient.This paper describes a new category of “intelligent” off-board diagnostics (OFBD) designed to cost-effectively supplement the diagnostic capabilities of OBD by providing the diagnostic information and functionality OBD is incapable of. It also examines the limitations to advancing the system architecture of OBD, and why OFBD is now the only solution to overcoming those limitations.Fully self-contained and infinitely software-configurable, the OFBD system is driven by a comprehensive VIN-based performance specification database, enabling both OEM systems developers and the automotive service industry to design and integrate into it virtually unlimited expert analysis capabilities. It connects in series with the vehicle system under test, enabling it to monitor every signal entering and exiting the PCM (ECM/ECU). The OFBD system is equipped with special circuitry to allow it to break signal circuits to take complete control of the vehicle system's various functions. This enables the OFBD system to isolate and verify the integrity of all the components and signal circuits comprising the vehicle system, including the PCM itself.