In the paper, we interest to smart actuators. External model has been defined in order to improve behavioural of actuator in presence of failures. The external model requires information from Fault Detection and Isolation algorithms. To complete the information providing to the users, we associate bond graph methodology to the external model in order to complete the information with physical knowledge. The objectives are to obtain self-diagnosis intelligent actuators. The proposed description will be applied to an intelligent actuator which integrates a control valve, a pneumatic servomotor and a positioner.