This paper proposes some principles for fault management of longitudinal control of automated vehicles in AHS. Systems faults may be broadly divided into software and hardware. Software fault management is briefly addressed. These faults can be avoided by proper controller design, rigorous algorithm development, correct and robust code construction, simulation and real-time run test. Emphases are put on hardware faults. Hardware faults which may appear in practice are classified according to their likelihood of appearance, impact on safety, robust stability within controller bandwidth and maneuverability. The most prominent cases are those when communication and/or radar are in fault. From control viewpoint, they have very strong impact on string stability. The main difficulties in these cases are: (a) Some or all of the three parameters: relative distance, speed and acceleration, are not directly available; (b) Measurements of these parameters contains some noise; (c) Filtering and estimation of these parameters lead to some time delay and discrepancy. General principle of control strategy for each fault case is proposed. Corresponding string stability of the platoon is briefly analyzed. Consideration in this paper is in higher level. To practically implement each of these strategies will be addressed in future works.