The glottal stop coda in Wu Chinese checked syllables diachronically weakens into non-modal phonation on the preceding vowel and finally disappears. It's crucial to capture the initial stage of this sound change when the glottal stop coda is realized as an abrupt glottal closure. Aiming to clarify the age-related differences in the phonetic realizations of the glottal stop coda, we detected the presence of the abrupt glottal closure at voice offset using speech and EGG signals from Shengzhou Wu speakers. Results show that the voice offsets in checked syllables produced by most old speakers remain aligned, indicating the sound change has not been initiated. However, the glottal stop coda is no longer realized as abrupt glottal closure in the younger generation. This study directly measures the glottal stop coda loss through the physiological basis of articulation, potentially providing insights applicable to abrupt glottal closure detection for other linguistic purposes.