The electrochemical behavior of 55% Al-Zn coated steel sheet, on which a very thin polymeric film (≈ 1 μm) was applied, was studied using electrochemical impedance spectroscopy (EIS). Use of a straightforward electric model to analyze the spectra obtained with different polymer films allowed correlation of the coating parameters and the physicochemical processes occurring on a microscale. Exposure to a 0.5% sodium chloride (NaCl) solution for variable time periods gave new insight into the mechanisms of protection and short-term degradation of the coating.