Fuel cell system and apparatus and method for diagnosing same

A fuel cell system comprising:

• a fuel cell stack made by stacking a plurality of cells, and the fuel cell stack being configured to generate power by being supplied with fuel gas and oxidation gas;
• a high-voltage battery configured to supplement the power generated by the fuel cell stack while being charged with the power generated by the fuel cell stack or being discharged;
• a converter positioned between the fuel cell stack and the high-voltage battery, the converter being configured to change an output voltage or an output current of the fuel cell stack;
• a power control unit configured to control the fuel cell stack to generate power when the fuel cell stack is requested to be diagnosed, the power control unit being configured to adjust the output current of the fuel cell stack to a predetermined current;
• and
• a voltage sensing unit configured to sense a voltage of the fuel cell stack or voltages of the plurality of cells included in the fuel cell stack in the state in which the output current of the fuel cell stack is the predetermined current;
• wherein the predetermined current comprises a plurality of currents determined by a maximum output current outputted in an End of Life (EOL) state of the fuel cell stack.