Aluminium alloys have become the material of choice for automotive heat exchangers due to their favourable mechanical properties and corrosion resistance. While the impact of homogenization temperature and duration on AA3xxx alloys has been studied, the specific effect of preheating holding time on clad AA3003mod alloys remains underexplored. This study investigates how isothermal soaking time influences the microstructure and corrosion resistance of AA3003mod alloy clad with AA4045, a configuration used in automotive brazing sheets. To replicate industrial production, hot-rolled and homogenised slabs underwent thermo-mechanical processing. Sandwich samples of AA4045/AA3003mod were preheated at 505 °C for 20, 30, 35, 40, 38 and 45 hours. Corrosion resistance was assessed using potentiodynamic through open-circuit potential (OCP) measurements and potentiostatic polarisation techniques in a 3.5% NaCl solution, with pitting quantitatively analysed via an Olympus Microscope equipped with a 3D imaging software and Scanning Electron Microscopy (SEM). The corrosion rates for all brazed samples exceeded the generally accepted standard of <0.1 mm/y. Pitting severity and current density peaked between 30 and 45 hours of homogenization, indicating reduced nobility. In contrast, samples homogenised for 20 hours exhibited minimal pitting, the shallowest pits, the most noble open-circuit potential, and the lowest current density, demonstrating that extended homogenization significantly deteriorates corrosion resistance of the roll bonded AA4045/AA3003mod sheets.