1997 Cadillac Catera what is the trasmision control module?

Transmission control unit or TCU is a device that controls the automatic transmissions. A TCU generally uses sensors from the vehicle as well as data provided by the Engine Control Unit to calculate how and when to change gears in the vehicle for optimum performance, fuel economy and shift quality. It is not a solenoid, but it does send signals to many different solenoids such as the shift solenoid.