Transmission Solenoids – How They Work and What to Do to Take Care of Them

There are some automotive terms that people simply don’t care to hear because they perhaps sound too technical, or send them into a daze of confusion and uncertainty. The problem is that some of these hard-sounding words are actually critical components that your car needs to run properly. A good example is “transmission solenoids” which will be the focus of today’s blog article.

What are transmission solenoids? What do they do? How do we make sure they don’t prematurely break on us? These questions and more we will endeavour to answer below:

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What are Transmission Solenoids? What Do They Do?

You are likely already aware that your car’s transmission is one of the most complex systems in the whole vehicle. It’s one of the reasons that full transmission repair and replacement can be so expensive, and why proper and regular maintenance is essential. One of the key components within an automatic transmission is the transmission solenoids.

If you drive a manual transmission car, then it’s more than likely that your car doesn’t have solenoids. They are electromechanical valves that manage the flow of fluid into and out of an automatic transmission and in doing so help to facilitate gear shifts. Depending on the electrical signals they receive, they open and close to allow or block the flow of transmission fluid and change the pressure within the transmission. It’s that change of pressure that is so critical to the ability to change gears.

Instead of using the driver’s own sense of when it’s time to shift gears, an automatic transmission relies on the Engine Control Unit (ECU) to signal when action is needed, and part of that action is taken up by the solenoids.

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How Do Transmission Solenoids Work?

So how exactly do your solenoids perform this key function for your automatic transmission? We’ll take a closer look in this section. The first key point here is that the solenoids work partly in conjunction with your car’s own speed sensors. The speed sensors are the key port of call for the car’s electronic control systems to know what actions might be needed, including (among things) when to change gears.

In a manual car, you don’t need this sensory technology, because you already have it in the form of the driver. The driver senses when the engine is revving too high and therefore when to shift upward, and vice versa. Without human senses, the automatic transmission needs help from sensors that communicate with your solenoids via electrical signals, telling them when to open and close.

The solenoids themselves are built with a wire-wrapped spring-loaded plunger. The wire wrapping is the vehicle through which the electrical signals are sent from the sensors and ECU. The actions of the solenoids provide the correct pressurisation and flow of transmission fluid to allow the many clutches to move smoothly and transition between gear ratios as you accelerate.

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Warning Signs that Solenoids are Failing

There are of course some components and systems on your car that if they fail it’s an annoyance but they don’t impact the overall safety and performance of your vehicle, such as your A/C compressor, or your infotainment system. You want them to work all the time, but if they don’t it’s not the end of the world. However, if your transmission solenoids are failing, then it’s time to take immediate action.

The first problem is knowing what the warning signs are. Below, we’ll cover the most common ones.

Sign 1: Downshifting Becomes a Struggle

Let’s start with what happens if you are braking or otherwise slowing, but your engine is continuing to rev at quite a high rate. This is showing some kind of delay or other malfunction that is negatively affecting your downshifting. This sign isn’t a definitive sign that the solenoid is broken, but it certainly indicates it’s experiencing difficulty. That difficulty, however, could be created by contaminated or old transmission fluid causing the solenoid to get stuck and thus not be able to open and close properly. Bad fluid can also delay the signals from the ECU.

Sign 2: You See a Check Engine Light (CEL)

The much-feared “Check Engine” light can of course mean many things, but if you see the CEL emerge in conjunction with other signs mentioned in our list, then the likely explanation for it is that your solenoids are experiencing some kind of malfunction. Another good way to be sure about this is to see if your car also goes into limp or a “fail safe” mode at the same time. If it does, then it is because there is something fundamentally wrong with the drivetrain, and that could be the solenoids.

Sign 3: You Can’t Get Out of Neutral

If you’re trying to move your car but it seems to be completely stuck in neutral gear, it’s another sign that the solenoids are not able to act upon information that they are receiving from the ECU. Very often this is not permanent but will create a significant delay between shifting the car into drive “D” and then moving along. This severe delay in shifting is very likely due to the lack of ability of your solenoids to open and close properly as instructed by the ECU. Once again, however, it is also more a sign that you need new transmission fluid than a sign that the solenoid itself is broken.

Sign 4: General Erratic Shifting

Finally, if you are sensing a general unevenness in your car’s ability to shift between gears, such as high revving in the engine but no response from the transmission, or continued revving when you are slowing down, then it should be enough of a warning sign to have your solenoids checked. Since the solenoids’ job is to maintain that fluid and smooth equilibrium between the many moving parts, it’s natural to suppose that unevenness is caused by problematic solenoids.

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What to Do When You See the Signs

If you have reason to believe that your solenoids are malfunctioning or not working properly because of bad transmission fluid, then you should take your car to the mechanic to do a full diagnostics check and see where the real problems are. One issue with solenoid faults is that what can appear to be a solenoid problem might actually be a connected part such as the transmission fluid, the speed sensor or even the ECU itself.

At any rate, it’s something you’re best leaving in the hands of professionals to ensure that the right repairs are carried out.