Near Field Scan Immunity (NFSI) is a powerful measurement method to diagnose susceptibility issues at printed circuit board (PCB) and integrated circuits (IC) levels. However, one limitation of this approach is the excessive measurement time required to build the susceptibility maps, which reveals the sensitive pins or traces of the device under test. This letter presents a pre-scan method based on a large-band injection in order to determine rapidly the more relevant scanning positions, the frequency range of interests and an estimation of the susceptibility level on each scanning position. The pre-scan provides the configuration parameters of the full NFSI scan in order to keep an acceptable test duration.