NOVELTY - The system has a hybrid measurement module with giant magnetoresistive current/voltage sensors (111-118) integrated on a same strip (100), and connected to a separate digital processing module (400). The measurement module has a printed circuit with an amplifying module (200) whose set of amplifiers (201-208) receives signals delivered by the sensors, and another printed circuit with a multiplexing module (300). The circuits are assembled with input-output connection terminals connected to signal exchange tracks formed on sections of the circuits and connected to connection devices (401, 402).    USE - Diagnostic system for measuring current or voltage of an electric generator embarked in a vehicle such as electric vehicle and hybrid vehicle, to monitor the voltage of fuel cells of the generator. Can also be used for monitoring a static electricity producing installation or electrolyzer, and managing charge of batteries or supercapacitors.    ADVANTAGE - The diagnostic system enables monitoring the fuel cell system, and optimizing and securing the control of the fuel cell system. The diagnostic system measures positive and negative voltages or low current in a highly precise, robust and intrinsic manner, even in environment with severe electromagnetic interference. The giant magnetoresistive current/voltage sensors assure galvanic isolation and safe fuse function in case of over-current, thus ensuring operating safety of the diagnostic system. The design of the diagnostic system enables miniaturization of constitutive components of the diagnostic system, so that the diagnostic system is compact, thus enabling simple integration of the diagnostic system in embarked applications. The design of the diagnostic system enables the giant magnetoresistive current/voltage sensors to be directly connected on the fuel cells of the generator. The sensors are autonomous, so that the sensors do not require additional components such as external power line and cable, for realizing the current or voltage measurement. The diagnostic system is inexpensive to fabricate, and consumes less energy. The diagnostic system has modular design, so that the diagnostic system is easily adapted to generators having large number of elementary cells. The design of the diagnostic system enables minimizing external noise sources.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of a diagnostic system.    Strip (100)    Giant magnetoresistive current/voltage sensors (111-118)    Amplifying module (200)    Amplifiers (201-208)    Multiplexing module (300)    Digital processing module (400)    Connection devices (401, 402)