In a previous paper we investigated the mechanism by which fully protically doped (emeraldine-salt form) polyaniline (PANI) protects stainless steel surfaces from corrosion in 1 M sulfuric acid solution. A mechanism was proposed, based on prior work by Deng et al., whereby passivation is achieved because the emeraldine-salt form holds the potential of the underlying stainless steel electrode in the passive region. This paper describes investigations of PANI-coated stainless steel surfaces exposed to more dilute sulfuric acid solutions. This is an interesting issue because while the solution becomes less corrosive as the concentration of the H2SO4 decreases, the concomitant change in pH also changes the protic doping level of the PANI film. UV-visible spectroscopy indicated that partially protic films are obtained upon exposure of PANI to solutions with H2SO4 concentrations in the range from 500 to 1.0 mM. Exposure to 0.1 mM H2SO4 yielded the protically undoped emeraldine-base material. We have found that both the partially protically doped PANI films and the totally undoped emeraldine-base films also hold the potential of the substrate stainless steel electrode in the passive region. Hence, the mechanism by which PANI protects the underlying metal surface from corrosion is independent of doping level.