A control method for controlling a transmission of a vehicle, the method comprising: receiving at least one measurement relating to a hydraulic lag of a continuously variable valve lift system that occurs in a cold condition, the continuously variable valve lift system being associated with an engine of the vehicle; determining, based on the at least one measurement relating to the hydraulic lag, an engine speed threshold above which engine power output is impaired as a result of the hydraulic lag; monitoring the engine speed; and generating an alert if the engine speed exceeds the engine speed threshold.