A powertrain assembly includes a continuously variable transmission having a variator, an input member, an output member and a torque converter clutch. An input sensor configured to receive a signal from the input member. An output sensor is configured to receive a signal from the output member. The assembly includes a controller having a processor and tangible, non-transitory memory on which is recorded instructions for executing a method of controlling the continuously variable transmission. If the torque converter clutch is locked, the controller is programmed to obtain respective readings at predefined time intervals which are collected for the respective signals from the input sensor and the output sensor, until a predefined time window is reached. First and second fast Fourier transforms are obtained of the respective signals. The continuously variable transmission is controlled based at least partially on the first and second fast Fourier transforms.