Apparatus and method for diagnosing vehicle electrical system

摘要

An apparatus for diagnosing the presence and location of faults within a vehicle's electrical system includes a signal generator for generating an a.c. test signal; a switching circuit connected to an interface between the system's ECU and the system's components for selectively and sequentially applying the a.c. test signal into each electrical lead therein; and a first detector connected to the system's common ground for detecting the system's response to the applied signals, thereby obtaining a set of transitory characteristics for the vehicle's electrical system. The apparatus further includes an EPROM within which a set of reference characteristics for the vehicle's electrical system is stored; a comparator means for comparing the detected transitory characteristics with the stored set of reference characteristics; and a diagnostic processor responsive to the comparator means for diagnosing the presence of a fault when the detected transitory characteristics of the vehicle's electrical system deviate significantly from the stored set of reference characteristics therefor. Upon diagnosing the presence of a fault within the vehicle's electrical system, a d.c. test signal is injected under the control of the diagnostic processor using the switching circuit only into the lead or leads of the interface deemed responsible for the deviant system output. A second detector likewise connected by the switching means only to those leads deemed responsible for the deviant system output detects the reflection of the d.c. test signal for use by the diagnostic processor in determining the location of any existing fault relative to the interface.