Malfunction detecting apparatus for on-vehicle charging system

An apparatus is provided for detecting a malfunction in an on-vehicle charging system provided with a generator (1) driven by an engine and a battery (4) connected with the generator via a charging line (2). The apparatus comprises a first control unit (7) controlling a generated condition of the generator and including a first voltage detector (9) detecting a voltage generated by the generator and a second control unit (6) including a second voltage detector (12) detecting a voltage across the battery. The apparatus further comprises a communication device (10,11) communicating, in the form of digital signals, via a communication line between the first and second control units, information about both the generated voltage and the battery voltage and a malfunction determination unit (15) determining whether or not a malfunction occurs in the charging system on the basis of the communicated information.