After having drawn up a state of the art on the theoretical feasibility of a system of periodic tasks scheduled by a preemptive algorithm at fixed priorities, we show in this article that temporal faults can occur all the same within a theoretically feasible system, that these faults can lead to a failure of the system and that we can use the data calculated during control of admission to install detectors of faults and to define a factor of tolerance. We show then the results obtained on a system of periodic tasks coded with Java Real-Time and carried out with the virtual machine jRate. These results show that the installation of the detectors and the tolerance to the faults makes an improvement of the behavior of the system in the presence of faults.