System and Method for MHSG Failure Diagnosis of Mild Hybrid Vehicle

An embodiment system for mild hybrid starter and generator (MHSG) failure diagnosis of a mild hybrid vehicle includes a data detection part configured to detect data for determining whether to activate a catalyst, and a controller configured to determine whether there is an MHSG failure using a deviation between a required torque and an actual operating torque of an MHSG after determining whether catalyst activation is needed and whether to start a stage of the MHSG failure diagnosis based on the data detected by the data detection part.