Abstract: The invention relates to a process and an apparatus for diagnosing defects in electric or electronic modules mounted in an automotive vehicle. This apparatus comprises a wire harness (2) adapted to divert status or control signals from a system to be tested, a formatting interface (15) comprising a plurality of calibrating modules arranged in parallel, a multiprocessor (21) connected to the formatting interface (15) and comprising a backup memory in which are stored, in real time, the defect signals, memories (25) for storage of a set of diagnostic programs corresponding to a group of systems to be tested, adapted to configure the multiprocessor (21) in such a manner as to dedicate it to the treatment of signals from a given system, and a man/machine interface (28) having means for displaying the contents of the backup memory and manual selection means.