Passive voltage contrast (PVC) is a conventional technique for open contact isolation. However PVC application is limited as it just can tell whether contact is grounded or floating . In this work primary current and voltage adjustment criterion is developed to break through this limitation. Adjusting the electron acceleration voltage (EPE) or current value can enhance differential voltage contrast effect. Hence, isolation of thin gate oxide leakage and N+/PW junction leakage can be distinguished in both contacts and metals. Voltage contrast (VC) image under varying primary current and voltage is demonstrated experimentally and discussed.