This paper is intended to present the design and implementation of a fault diagnostic and fail safe for an electronic parking brake system. The fault diagnostic function includes an input signal, output signal, and fault diagnostic using a microprocessor. The fault diagnostic function determines faults in the main microprocessor. The EPB has the function of the microprocessor and the permissible range of system control. The input signal detects faults using the voltage of the switch pole, the output signal defines faults using the current level of the motor. The microprocessor judges failure using internal software. And a sub microprocessor monitors the status of the main microprocessor using periodic communication between the main microprocessor and the sub microprocessor. Also, the microprocessor controls the output signal when emergencies occur. When the sub microprocessor judges that the main microprocessor and the system recovers from the fault. The safety and reliability of the EPB system can be improved using the proposed fault diagnosis system.