This study investigates the impact of both direct and indirect moisture ingress into an automotive engine control unit(ECU) on vehicle behavior and operational safety. Two experimental conditions were examined: exposure to an environment with 100% relative humidity(indirect ingress) and direct injection of 1.0~2.0 cc of water onto the ECU(direct ingress). The results showed no abnormal behavior under indirect moisture conditions. However, direct moisture ingress caused engine malfunctions, warning light activations, and irregular vehicle behavior. Notably, the vehicle's safety logic functioned as intended, resulting in engine shutdown without leading to unintended acceleration. These findings provide quantitative data valuable for future reliability assessments of ECUs and investigations into sudden unintended acceleration phenomena.