With the help of automated model generation (AMG), high level modeling (HLM) of analog circuits is able to provide useful speedup and acceptable accuracy compared with standard SPICE-level circuit simulation. Unfortunately, this is not the case for high level fault modeling (HLFM) and high level fault simulation (HLFS). This is still a critical issue that industry is facing in reducing analog testing cost. We present a novel algorithm using a fusion of Chebyshev and Newton interpolating polynomials (CNIP) in nonlinear state-space (ss) termed AMG-CNIP for HLFM in analog circuits. It is written in MATLAB and the hardware description language (HDL) VHDL-AMS, respectively. The properties of AMG-CNIP are investigated by modeling nonlinear transmission line circuits using transient analysis. Results show that the AMG-CNIP models can handle both linear and nonlinear fault simulations with reasonable accuracy, and simulation speedup is achieved compared to standard SPICE-level simulations. © 2014, Springer Science+Business Media New York.