The automatic transmission solenoid is a solenoid valve that opens and closes the oil channels of the valve body, through which the ATF is supplied to the mechanical elements inside the gearbox.
An ECU box – automatic, controls the operation of the solenoids. The control unit sends electrical signals to the solenoid, thereby opening or closing the valve. This allows you to control the pressure of the transmission oil when it is supplied to the clutches (automatic transmission clutch elements).
Thanks to the operation of the solenoids in the automatic transmission, gears are shifted, and the blocking of the gas turbine engine (torque converter) is turned on and off.
The automatic transmission solenoid device
If we talk about the simplest design, the solenoid is an electric valve for ease of understanding. In a nutshell, there is a metal rod in the body, on which a spiral is wound. A current flows along the indicated spiral.
This rod in the body is movable, under the influence of the current moves from the end of the spiral to its beginning. Also, a spring acts on the rod, which closes the valve.
The solenoid is installed in the valve body (hydraulic valve plate). The valve is inserted into the channel, and electrical wiring is also attached to it for connection to the control unit. As a rule, 4 or more solenoids are installed in an automatic transmission (depending on the number of gears, the design features of the box, etc.).
Solenoid types
At the initial stage, solenoids for automatic transmissions are performed only by opening and closing the valve body channels. Further, according to the principle of operation, the solenoid began to resemble an electromagnetic valve (hydraulic valve).
The device received a separate oil channel and a ball-type valve responsible for closing this channel. Further, the technology was developed, which made it possible to create a new generation of solenoids.
In such a device, the ball in the open position allows the oil to pass from the first to the second channel and in the closed position from the second to the third. As a result, it was possible to effectively turn on and off the friction clutches (clutches).
The next stage of development was solenoids with the possibility of additional regulation, similar to a valve. Such valves have an internally curved cross-section. Having received an impulse from the ECU, the solenoid section may open slightly or close slightly. This solution allowed for even more flexible oil pressure control.
We also add that the solenoids are ball, spool (with a valve – spool), linear solenoids, VFS solenoids, etc. By the way, the resource of the latter is noticeably lower than that of linear ones.
Also, solenoids can perform different functions. For example, if you separately study the device of hydromechanical automatic transmissions, the EPC / LPC solenoid is “main” since oil passes through it to other solenoids and valve body channels.
The automatic transmission also has a TCC solenoid. This solenoid is responsible for blocking/unblocking the gas turbine engine. Hot and dirty oil from the torque converter passes through it so that this element often fails. The Shift solenoid acts as a speed switch; there are also hydraulic plate control solenoids, etc.
Malfunctions and repair/replacement of automatic transmission solenoids
First of all, the service life of the solenoids directly depends on the condition and quality of the automatic transmission oil. If the oil is dirty, the solenoid valves are clogged with automatic transmission wear products, various deposits, etc.
As a result, the valve begins to “wedge” or “hang”. Naturally, the box stops working correctly, jerks, automatic transmission kicks appear, individual gears do not turn on, etc.
Also, a common cause of problems with solenoids is the wear of channels and plungers. It is often noted that the springs lose their elasticity, cracks appear in the housing, and problems arise with the solenoid winding.
Often, the resource of the most reliable solenoids is no more than 450 thousand km; the cheaper “lightweight” versions work properly no more than 250 thousand km. The parts themselves often wear out inside the solenoids (bushings, valves, plungers, balls, etc.).
Diagnostics and replacement of the box solenoids – an automatic machine is needed if the automatic transmission does not work correctly. When diagnosing, you should check the solenoids separately. Depending on the type of automatic transmission, each of them is responsible for certain functions.
For example, in a simple “automatic” for 4 gears, there are usually 4 solenoids. In this case, the first solenoid is responsible for switching on the first and second gears, the second for the third and fourth gears, the third valve controls the blocking of the gas turbine engine, the fourth is responsible for the brake band.
If the driver noticed that there were problems when switching from second to third or from first to second gear, you should study the device of a particular automatic transmission at the initial stage. Then you can more accurately guess which solenoid is faulty.
Also, a problem with solenoids often manifests itself in the form of an error flashing, a faulty AT warning lamp on the instrument panel, etc.
In this case, the errors must be read with a scanner and decoded, as well as you must check the valve body and solenoids. The solenoids are tested for resistance and also flushed or blown out with compressed air.
Solenoid repair in an automatic box is often not provided. Otherwise, regarding the repair of solenoids, the task becomes more complicated since this part in modern automatic transmissions is non-separable.
In practice, this means that the solenoid, in this case, can only be rinsed and cleaned. If you can disassemble the solenoid, then its winding can be replaced, as well as a more thorough cleaning of all valve elements.
Replacing the solenoids in the box – the machine is performed after diagnosing their performance. For replacement, it is necessary to remove the valve plate, remove the faulty valve and install a new one. After that, the valve body is installed in place, the tightness is checked, ATF liquid is poured, and then the automatic transmission operation is tested.
« Back to Glossary Index