A transmission solenoid controls the flow of transmission fluid into different parts of the transmission system. Basically, it is an electronically controlled valve that opens and closes to let the transmission fluid flow or to stop the flow of the fluid as needed. This means a malfunction of the solenoid interferes with the functions of the transmission fluid, and this leads to transmission problems. Here are some of the things that should tell you your transmission solenoid has malfunctioned:
Delay in Shifting
Although a gear shift seems to happen instantly, it involves two distinct stages. The first stage is the activation of the clutch while the second stage is the engagement of the gear. A malfunction of the solenoid may create a noticeable delay because the two processes won't run instantaneously. In that case, there may be a lull between the two processes during which your car will be behaving as if it is in neutral gear. This happens when the solenoid doesn't receive the right electrical power and the gear engagement delays.
You should also suspect a solenoid problem if you are having difficulty downshifting the car. If this is happening to your car, then it will continue revving or even rolling forward at a slow speed when you try to stop the car. As you can imagine, this is a pretty dangerous problem to have because you can collide with another motorist. It is caused by a stuck solenoid that prevents transmission fluid from entering the transmission valve to engage the right gear.
Difficulty Changing Gears
A malfunctioning transmission solenoid may also make it generally difficult to shift your gears. As previously mentioned, the electronic solenoids are responsible for controlling the flow of transmission fluids into the transmission valves for pressurizing gears. If a solenoid is acting up, then it may send too little or too much fluid into the transmission valves, and both actions may affect the operations of the gears.
Random or Unpredictable Shifts
In some cases, your transmission solenoids may even cause your car to shift gears randomly without any input from you. You may even find your car shifting one of its gears. For example, if one of the transmission valves is not getting pressurized properly, it may get skipped during gear shifts. In fact, you may find the car shifting to a different gear (where the transmission pressure is adequate) when you try to shift.
As you can see, the problems associated with transmission solenoid malfunction are serious. Therefore, consult a transmission or automotive repair shop as soon as you suspect the solenoid is acting up.