<p>An active model-free sensor fault-tolerant control approach is presented in this paper. The proposed method is based on a model-free controller that has demonstrated an effective ability to work without any analytical model knowledge. The active fault-tolerant control procedure has three stages: firstly, the model-free controller is designed using an ultra-local model; secondly, this ultra-local model is used to detect and estimate the sensor fault; thirdly, the obtained estimation is used to adapt the control law according to the sensor fault. The aim of the proposed active fault-tolerant control procedure is to ensure that the regulated output, but not the measured one, tracks the desired trajectory despite the occurrence of a sensor fault. Additive or multiplicative sensor fault is considered for systems that have a linear relationship between control input and system output for any reached steady state. This kind of system includes linear ones and some specific nonlinear systems. The developed methods are validated via numerical simulations for unstable linear and nonlinear systems, with and without saturation of the control input.</p>