Abstract: A method is provided for sensing leakage in a clutch cylinder system in a vehicle including an automated manual transmission, wherein the clutch cylinder system includes a clutch cylinder provided with a reciprocable piston, whose position is sensed by a position sensor and affected by pressurization of the cylinder by opening or closing at least one air inlet valve and by opening or closing at least one air outlet valve and wherein the clutch is in an engaged position when there is no air pressure in the cylinder. The method includes the steps of: a. closing the at least one inlet valve and at least one outlet valve for compressed air; b. sensing a position of the piston during a predetermined time span, and, c. if the position has changed more than a predetermined allowable position change, sending an error signal to an onboard diagnostics system or a signal light in the vehicle.