What Is a Transmission Shift Solenoid?

The transmission shift solenoid is an on-off electro-hydraulic valve that controls and directs fluid flow inside a transmission. Its main field of application is in electronically controlled transmissions

To actuate the gear shift, a transmission shift solenoid is composed of a solenoid pintle, a spring and an electric coil winding. The spring loaded plunger is wrapped in a coil of wire that when energized pulls the plunger inwards, thereby opening or closing the hydraulic circuit. When there is no supply of power to the solenoid, the plunger is pushed outward by the spring to its original position.

This mechanism of opening and closing enables pressurized transmission fluid to move through the different channels in the valve body, and to different bands within the planetary gear set. This fluid is used to for the clutch and band brakes.

The solenoid communicates with the car engine sensors or the transmission control module through electronic signals. The sensors decide when it is time to shift the gears depending on the vehicle and speed of the engine. The transmission solenoids are the mechanical actuators controlled by the transmission control module based on the input from the sensor that facilitate the smooth application of gears.