Abstract In this work a nonlinear dynamic and mathematic model for the position control of a hydraulic actuator with internal leakage was developed, simulations were made and a basic PID control in order to check the actuator behaviour. An internal leakage emulator was installed bypassing the two chambers of the hydraulic cylinder. Time and position data were acquired via Quanser Q8-USB and saved for modelling and validation purposes, sinusoidal and square signals and both for four fault conditions. Data were classified through MATLAB Simulink algorithm having in consideration parity equations and residual generation, obtaining a high level of validation for the proposed model and the desired responses and fault detection, diagnosis and classification.