In this paper, we present a method for the optimal selection of test points and the generation of test frequencies. Our method is based on large change sensitivity analysis with element level analysis operating in the frequency domain. The fact that the deviation of individual components can be set to arbitrary value ranging from zero to infinity, high fault coverage and enhancement in the overall circuit testability are ensured. The proposed method can diagnose both catastrophic and parametric faults. Our results show that both single and multiple faults can be located within small to medium size circuits. The computation is realized by combining the evaluation before test with a symbolic math package. This combination provides low computational cost and proves to be efficient comparing to conventional fault diagnosis methods. Keywords: fault diagnosis, analog circuits, large change sensitivity