Modulator vs TPS

Some hydraulic transmissions use modulators to control the throttle valve. They mount to the transmission case and contain a spring and a pin that moves in proportion to the engine's manifold vacuum. Adding a stronger spring or a longer or shorter pin will cause a firmer or softer shift. These pins come in different lengths to adjust or modify shift feel. They have been replaced by throttle position sensors in today's electronically controlled transmissions.

Most Throttle Position Sensors are also adjustable. Rotating the sensor left or right will change the signal sent to the TCM. The modulator's signal is modified by manifold vacuum, and the TPS provides the throttle plate's angle. Both sensors affect throttle pressure. Modulators are found on hydraulically controlled transmissions, and throttle position sensors are found on modern electronically controlled transmissions.