While manual transmissions make use of the clutch to change gears, automatic transmissions rely on a complicated hydraulic system for shifting, and the transmission solenoid is especially important for this process. Transmission fluid is directed throughout the valve body by various transmission solenoids–such as the transmissionshift solenoid, lockup solenoid, or transmission control solenoid (there’s also a torque converter clutch solenoid)–that either open or close hydraulic valves to regulate fluid flow. Speed sensors around the engine are responsible for activating the solenoids.
As you can guess, the transmission solenoid is a required component of a functioning transmission, and any solenoid that starts malfunctioning only spells trouble. So today we’ll explain its function, common problems that can occur, and everything you need to know about replacement here.
What Does a Transmission Solenoid Do?
The automatic transmission relies on bands and clutches to change gears, and the only way they can be applied is by fluid pressure. The transmission solenoid is responsible for opening or closing valves in the valve body to allow transmission fluid to enter, at which point the fluid can do its thing and pressurize the clutches and bands. Solenoids consist of a spring loaded plunger wrapped with a coil of wire, and communicates with the car’s engine sensors or the transmission control module (TCM) via electronic signals to either open or close.
Sensors determine when it’s time to shift gears depending on vehicle and engine speed. If the transmission solenoid is energized, the plunger opens and allows fluid to pass while a solenoid that is not receiving power is closed in its normal position. So while the various engine sensors determine when the gears should shift, it is the job of the transmission solenoid to act out the actual shifting.
Common Transmission Solenoid Problems
You can probably guess already that a lot of shifting problems can be attributed to a malfunctioning shift solenoid since they are responsible for regulating fluid pressure. A transmission that receives too much fluid pressure will have rough shifting, while not enough can cause clutch plates to overheat.
An electrical malfunction will cause the solenoid to act erratically and when the check engine light comes on, a quick scan of the car’s computer should tell you what’s wrong. If you do receive an OBD code, you can bring your transmission to a certified mechanic to have it diagnosed and fixed. If the check engine light doesn’t appear but you are experiencing shifting problems, the problem with the solenoid is most likely a mechanical issue which replacement of the part should solve.
These are typical signs of a malfunctioning transmission solenoid:
A delay in shifting – A delay in shifting can last as little as a few seconds or even longer, possibly a minute or longer. During this period your car will act as if it’s in neutral and you won’t be able to accelerate.
Transmission does not downshift – A functioning transmission automatically downshifts as it slows down and changes to first gear once you reach a complete stop. However, a bad shift solenoid will cause your transmission to downshift uncontrollably or not at all.
Transmission does not shift into the right gear – A defective solenoid can also cause your transmission to shift to the wrong gear, skip a gear, or shift back and forth unpredictably. Take notice of these changes as you attempt to shift as any of these reasons warrants a look at the solenoid.
Transmission Solenoid Replacement and Cost
If you’ve scanned the computer and have an OBD code relating to the solenoid, or you’ve isolated the problem to a mechanical issue with it, then transmission solenoid replacement might be necessary. Oftentimes, replacing a transmission solenoid will take no more than 2 hours, and repair shops on average charge $60 to $100 per hour for labor, not including cost of parts (a replacement solenoid should cost you no more than $200) or shop fees. However, costs can vary depending on what specific transmission solenoid you’re looking to replace. Some solenoids can only be replaced by removing the complete valve body, which can take a significant amount of time and therefore can be expensive because of shop fees per hour.