In low temperature PEM fuel cells, CO poisoning of the anode catalyst lead to severe performance losses. To investigate the CO poisoning effects, researchers employ electrochemical impedance spectroscopy (EIS), based on electrical equivalent circuits (EEC) models. But, EEC models do not correlate to the physicochemical processes in the cells and are valid only in the vicinity of the operating point. In this work, the CO poisoning model developed by Springer. et. al. (2) is employed to generate the transient behavior and the EIS of a completely poisoned anode by numerical techniques, in the galvanostatic and potentiostatic modes. Linear and bridge adsorbed states of CO on Pt surface are incorporated. The simulated results are compared with the experimental data from literature. The model is found to adequately replicate the experimental data in a qualitative manner. The manifestation of nonlinear effects due to the application of large amplitude perturbation signal is also examined. © The Electrochemical Society.