The transmission is the part of the vehicle that makes the wheels turn. The transmission has several gears that move the car forward and backward at varying speeds. There are automatic transmissions that shift from between driving gears automatically based on the speed demanded by the driver. Manual transmissions require the driver to manually switch between gears based on the speed desired. Transmission modulators are a component of automatic transmissions. It is an electronic module that takes input from several different sensors about the state of the transmission at any given time and at any speed. These are translated into signals to make any necessary adjustments so that the transmission can operate optimally. Transmission modulators are basically computers that can affect change in the system if it is needed. When the modulators malfunction, it is likely that the transmission will not function well and may shift hard or RPMs will run high until the delayed gear shift.