Autonomous underwater vehicles (AUV) are rapidly becoming useful and versatile tools in the ocean environment. They have only recently matured to the level of commercial viability, but there is currently recognition of the need for AUV, and an expectation of increased benefit from using these vehicles. In order for AUV to be firmly established as a viable, mature technology there are several issues that need to be addressed, not the least of which is reliability. A systematic study was made involving simulations of a vehicle under fault conditions to identify the vehicle behaviours typical of such fault conditions. The simulation tool used is a linear model of the dynamics of the Canadian Self-Contained Off-the-shelf Underwater Testbed (C-SCOUT), and the maneuvers used were those most likely to be desired during normal operation; holding course, a controlled dive, and a turn in the horizontal plane, C-SCOUT is typical of many cjurrent AUV, therefore the results of the study are appplicable in a qualitative sense to a number of vehicles.