The corrosion protection of 2024 T3 aluminum alloy by 1,2,3 benzotriazole (BTAH) was investigated in sulfate-containing chloride solutions with electrochemical noise measurements and scanning electron microscopy (SEM) observations. At high concentrations of chloride ions, BTAH prevents uniform corrosion of Al 2024 by protecting the Cu-rich particles. This effect was shown by the decrease in amplitude of the potential and current fluctuations after BTAH addition and confirmed by SEM images. In contrast, the inhibitive effect of BTAH could not be monitored by the noise resistance R-n and the noise impedance Z(n) at 0.01 Hz, which is equal to the modulus parallel to Z parallel to of the electrode impedance at this frequency. These two quantities did not vary when the BTAH was added to the aggressive solution. This is because the potential and current fluctuations are provoked by local corrosion events whereas R-n and parallel to Z parallel to estimate the mean corrosion behavior of the electrode. At low chloride concentrations, BTAH protected the material efficiently against localized corrosion, which could be identified in the BTAH-free solution by R-n values lower than the Z(n)=parallel to Z parallel to values at 0.01 Hz.