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Impedance measurements were made on an electrochemically polarized AISI 316L stainless steel in a 5% NaCl solution at room temperature. Limited information about this electrochemical method is available in the literature. Three polarization sweep rates, 0.10, 0.30 and 0.40 mVs⁻¹ were tested. Nyquist plots at the pitting potential regions show three capacitive loops. A deconvolution method combined with a complex non-linear least squares program was used to determine the individual components of the equivalent circuit and transfer functions. Negative capacitance and resistances were obtained. The impedance data do not satisfy Kramers–Kronig transforms. It is clear that stability conditions are not met for electrode processes indicating surface relaxation.