Abstract: A self-diagnosing apparatus for a vehicles capable of reliably storing diagnostic data on high priority malfunctions. A control unit comprises a CPU and a RAM for storing stores contents even when an ignition key is turned off. The self-diagnosing apparatus detects a plurality of malfunctions. The plurality of malfunctions are classified into high priority malfunctions and low priority malfunctions. The RAM has a plurality of storage areas including a first frame and a second frame, the first frame being made to correspond to high priority malfunctions and the second frame to low priority malfunctions. The CPU inputs diagnostic data from each section of the motor vehicle necessary for analyzing instrument malfunctions and updates the stored contents of each area of the first and second frames.

Abstract: A bidirectional light transmission system comprises a transmitting station having a light source for intensity-modulating a transmission signal, a first light branching portion for branching intensity-modulated light of the light source in a predetermined ratio and a first light receiving portion, and a receiving station having a second light branching portion, a light phase-modulating portion, a light reflecting portion and a second light receiving portion.