<p>Diamond-like carbon (DLC) coatings are attractive for corrosion protection, but defects inherently introduced during arc ion plating can create localized electrochemical pathways that limit their effective barrier performance. This study investigated pulse-based electrochemical oxidation in a citric acid–H₂O₂ electrolyte as a post-treatment strategy for improving the corrosion resistance of DLC-coated 316&#xa0;L stainless steel. Surface analysis showed that the treatment progressively reduced roughness and nodular surface features, while electrochemical measurements revealed a clear concentration-dependent response with an optimum at 5000 ppm H₂O₂. At this condition, the corrosion current density decreased from 1.105 to 1.27 × 10^− 4 µA/cm² compared with the untreated specimen, indicating a substantial suppression of corrosion activity at defect-accessible regions. Electrochemical impedance spectroscopy further supported this optimum response, as R_coat and R_ct showed relative increases of 71.31% and 336.83%, respectively, compared with the untreated specimen. These results indicate that the 5000 ppm H₂O₂ treatment enhanced both the coating barrier resistance and the resistance to interfacial charge-transfer processes. In contrast, the electrochemical response deteriorated at 10,000 ppm H₂O₂, demonstrating that the beneficial effect of oxidation does not increase monotonically with oxidant concentration. These findings identify an optimum oxidation window in which defect-mediated electrochemical activity is most effectively suppressed and establish electrochemical oxidation as a defect-targeted post-treatment strategy for upgrading the corrosion resistance of DLC-coated stainless steel.</p>