stand mixer problem

This is a KitchenAid 5 qt. stand mixer Pro Plus. When it’s turned on, whatever speed selected, it runs faster than it should for about 2 seconds then shuts off. I’ve replace the speed control board and the motor, and neither of those solved the problem. I’ve ordered the speed sensor which is the only other part left to replace but it is on back order. What’s the problem??? Could it be the speed sensor?