This unit describes the skills and knowledge required to diagnose complex faults in hybrid, plug-in hybrid and battery electric vehicle (HEV, PHEV and BEV) network management systems and determine the repair action necessary to restore system performance. The systems used vary based on the work context. It involves confirming the existence of a fault, developing a diagnostic testing strategy, diagnosing the cause of the fault, reporting conclusions and making repair recommendations. Importance is placed in the unit on applying electrical safety procedures when working on high voltage (HV) rechargeable energy storage systems (RESS). Complex faults are outside the normal scope of a technician’s diagnosis and repair work. They include intermittent faults, multi-system faults, faults introduced as a result of system repairs, and indirect faults caused by the influence of external systems, requiring the application of complex diagnostic processes to resolve.The unit applies to those who work in the automotive service and repair industry. No licensing, legislative, regulatory or certification requirements apply to this unit at the time of publication.