What Do Transmission Solenoids Do?

Most manual transmissions do not have solenoids. Automatic transmissions, however, rely on solenoids to facilitate gear changes. Solenoids are electro-hydraulic valves that control one or more gears depending on the transmission and build of the car. They control the flow of transmission fluid by opening or closing based on electric signals

When a solenoid opens or closes, it changes the pressure within the transmission, allowing your car to change gears. While the driver controls gear changes in a manual transmission, automatic transmissions rely on the car’s speed sensors and Engine Control Unit (ECU) or Transmission Control Unit (TCM) to judge the speed of the car and signal necessary changes, including controlling transmission solenoids to change your car’s gears.

What Are the Warning Signs of Failing Solenoids?

Typically, a failing solenoid will not be an emergency transmission repair and you will be able to continue driving your car for a while. However, you will notice certain signs when driving your car. As far as transmission services go, this is a relatively simple fix when you bring your car promptly to local expert mechanics as soon as you notice any of these signs.

Delayed or Erratic Gear Shifting

If you notice it taking a bit longer for your car to shift gears, it could be a failing solenoid. Dirty transmission fluid can cause solenoids to stay stuck open or closed, thereby making it more difficult for your transmission to change gears when it needs to.

You Can’t Downshift and/or Your Car Revs When Braking

This may also be a failing solenoid due to dirty transmission fluid. If a solenoid is stuck open or shut because of buildup or contamination within the transmission fluid, it will not react as easily to signals from the ECU or TCM telling it that you’re slowing down.

Your Transmission Gets Stuck in Neutral

Another sign that you have one or more solenoids that are stuck open or closed due to dirty transmission fluid. While the solenoid is receiving the signal to shift into first gear, it is unable to carry out the required action.

Your Check Engine Light Comes On

This is a sure sign that you need to take your car in to a repair shop to be diagnosed. Also, if you reach the point where your check engine light comes on, your transmission may go into limp or Fail Safe mode, meaning you will have even more trouble driving your car. You will have limited power and available gears so there will be a noticeable change in how your car drives.