This work focuses on fault diagnosis of electronic analog circuits. A fault diagnosis system for analog circuits based on wavelet decomposition and artificial immune systems is proposed. It is capable of detecting and identifying faulty components in analog circuits by analyzing its impulse response. The use of wavelet decomposition for preprocessing of the impulse response drastically reduces the size of the detector used by the Real-valued Negative Selection Algorithm (RNSA). Results have demonstrated that the proposed system is able to detect and identify faults in a Sallen-Key bandpass filter circuit.