Condensation of diesel exhaust gases inside an exhaust- or turbo manifold may occur during cold-start and cooling of an engine, resulting in acidic liquid covering the oxide surfaces inside the manifolds. In the present study, the interaction between a chloride-containing exhaust-gas condensate of pH 2.4 and oxide scales formed on a 25Cr/20Ni cast stainless steel in air and in two different exhaust environments, 10%H2O-5%O2-85%N2 and 10%H2O-5%CO2-85%N2, at 900°C has been examined by means of electrochemical impedance spectroscopy, EIS. Interpretation of impedance spectra was coupled to oxide scale structures, revealed by SEM, EDX, XRD and GDOES, and to metal release studies using ICP. It was observed that the acidic condensate caused oxide spallation, followed by corrosion of the underlying metal surface for all test samples. The metal release rate of the oxide scale and underlying alloy was found to decrease at longer immersion times (>1h), most likely due to precipitation of corrosion products on the surfaces. EIS combined with equivalent circuit fitting showed to be a useful technique in describing the electric properties of the oxide scales, suggesting oxidation in H2O/O2 to result in formation of oxide scales being more resistive compared to the other environments. This was coupled to higher thickness and higher defect density, which correlated well with oxide scale analysis.