1. A fail-to-neutral diagnostic method for a transmission including a variator, the method comprising: monitoring a state of a pressure differential valve fluidly coupled to a high side pressure applied to at least one actuator coupled to at least one corresponding roller of the variator and also fluidly coupled to a low side pressure applied to the at least one actuator; determining from the state of the pressure differential valve a variator torque sign corresponding to whether torque transferred by the at least one roller is positive or negative; determining an expected variator torque sign based on current operating conditions of the transmission; and commanding the transmission to a true neutral condition if the determined variator torque sign is different from the expected variator torque sign.