A method for activating a freewheel function of a vehicle, where the vehicle is equipped with an auxiliary brake, an auxiliary braking control for controlling the braking power of the auxiliary brake between an auxiliary brake not-active position and at least one auxiliary brake active position, at least one engine, at least one wheel driven by the engine via an automated mechanical transmission, an accelerator pedal for controlling the driving torque of the engine. When deactivation of the auxiliary brake occurs due to manual positioning of the auxiliary braking control to the auxiliary brake not-active position, the freewheel function is automatically activated if a freewheeling condition is sensed.