Transmission solenoid valves, solenoids, and connectors

What are automatic transmission solenoids?

The transmission solenoid, or solenoid pack, is a type of electromagnetic valve whose function is to control the Automatic Transmission Fluid, ATF flow, or transmission flow. Solenoids are usually installed in packages in the transmission control unit or valve body. If the flow path is hindered, the transmission will not work properly.

ATF controlled by solenoid valves pressurizes the transmission bands and clutches, making gear changes easier.

Automatic Transmission Solenoid Types

In automatic transmissions, there are different types of solenoids, such as:

• Lock solenoids. It´s role is to block the passage of energy.
• Control solenoids. It´s a type of valve that controls the pressure in the transmission to ensure the system´s performance.
• Shift solenoid. They are valves that operate dipped in the transmission fluid and control gear changes.
• Torque converter clutch solenoid. It´s a valve that prevents the ATF from escaping and losing pressure, preventing the transmission from overheating.

How Do Transmission Solenoids Work?

Inside the car's engine, sensors constantly monitor operation and analyze what needs to be adjusted. When a vehicle needs to change gear, the sensors send signals to the transmission control unit, which in turn signals the solenoids to open or close and allow the gear change to take place. 

Shift solenoids have a spring wrapped with a wire inside, which connects to the speed sensors and the transmission control unit. That way the transmission signals can be received. 

Information transmitted by the transmission control unit allows upshifts/downshifts to be executed through a signal to one of the solenoids so that the plunger opens and ATF flows into the valve body and pressurizes bands and clutches to make the gear change. 

The vehicle's computer controls the solenoids in different ways. For example, they can be open or closed through a direct 12v signal, control one or more gears, or switch the plunger through the ground loop. 

Parts of Transmission Solenoids

Transmission solenoids have nine parts that work together to make this component work properly. These parts are: 

• The body´s valve
• A port of entry
• A port of departure
• The solenoid coil body
• The coil winding
• Lead wires
• A plunger or piston
• A spring
• An orifice