The 6l80 transmission pressure control solenoid is responsible for regulating the pressure inside the transmission. To test it, you'll need a pressure gauge and a way to connect it to the transmission. Once you have that, you can start the engine and let it idle. With the engine running, you'll need to check the pressure inside the transmission. If it's within the normal range, then the pressure control solenoid is working properly. If the pressure is too high or too low, then the pressure control solenoid may need to be replaced.