Modern automatic transmissions are basically designed with pressurized hydraulic fluid to adjust gears. Each time a change of the gear is required, the computer of a vehicle will activate a transmission solenoid, which helps to direct transmission fluid to the valve body to involve the proper gear. When one of those electro-mechanical valves go wrong, then all types of transmission issues can occur. So let’s take a look at the transmission solenoid and some of common issues associated with it.
How do transmission solenoids work?
As you are going down the road, the computer of your car will analyze information being provided by engine speed sensors and car speed sensors. Based on these data, the TCM (transmission control unit) or the ECU (engine control unit) performs the proper downshift or upshift by transmitting a signal to one of the transmission solenoids. These shift solenoids are often made with an interior spring-loaded plunger, which is generally covered with wires. When this wire’s coil receives the electrical charge from the ECU or the TCM, it makes the plunger to open, letting transmission fluid flow to the valve body as well as pressurize the expected bands and clutches. When this occurs, the transmission adjusts gears while you are continuing down on the road.
The computer of a vehicle can regulate the shift solenoid in some ways. If the car is designed with a specific TCU, it could close or open the hydraulic circuit by applying a direct 12-volt signal. Otherwise, the ECU could control the plunger of the solenoid by turning on and off the ground circuit. A transmission solenoid can be often used to regulate a single or multiple gears, depending upon the complication of the model.
Common signs of problem in a transmission solenoid
A transmission solenoid could go wrong due to some electrical problems or dirty fluid, which causes the shift solenoid to get stuck when open or closed. Any changes in the pressure of the transmission can also lead to numerous issues, including:
1. Transmission does not downshift
When the transmission does not downshift, one of the transmission solenoids might get stuck open or closed, which eventually prevents the fluid from flowing into the transmission valve body to press the appropriate gear.
2. Erratic Shifting
If you are facing a defective transmission solenoid, the gearbox could skip up or down a gear as well as repeatedly move back and forth between gears, or become stuck in the gear and do not shift.
3. Stuck in neutral – severe delay in shifting
To make an electronically regulated automatic transmission change gears, the transmission solenoid should be able to control the pressure of the fluid to activate the correct gear. When the transmission solenoid receives too little or too much electrical current, or when dirty transmission fluid has made it to be stuck open or closed, the engagement of the gear might become delayed or difficult, which could eventually make the transmission to work as though it is locked temporarily in neutral.
As the solenoids are often connected to the electrical system of a car, the ECU would apply an error code and turn on the check engine light when something fails. If this occurs, the transmission could go into a fail or limp mode in which it would only engage the second or third gear to control the car speed without stopping it.
Therefore, the first thing that a technician needs to use a scan tool to look at the error code. By doing this, the mechanic could determine the cause of the problem in the transmission solenoid. It would be as complicated as a defective solenoid pack ( a group of separate shift solenoids ) or as simple as a terrible ground.
Replacement cost of a transmission solenoid – parts and labor
In most situations, solenoids are connected to the valve body in the oil pan. Depending on the car model that you are driving, the mechanic might only replace the failed transmission solenoid. But sometimes, the solenoid comes in various unit packs so if there are any issues with one, the whole pack needs to be replaced. Typically, this task would take from 2 to 4 hours to complete, and the bill is generally from 60 USD to 100 USD per hour. The average total expense to diagnose and change a transmission solenoid would range from 150 USD to 400 USD.
Depending on the model and make of the car, you would expect to pay from 15 USD to 100 USD for each transmission shift solenoid, while a pack could cost range from 50 USD to 300 USD.
Range of replacement cost
15 USD to 100 USD
50 USD to 300 USD
120 USD to 400 USD
250 USD to 600 USD
Even though it is usual for a transmission shift solenoid to wear out over time, you could extend its life by replacing the transmission fluid at the recommended intervals of the manufacturer. This will help to clean out all of the sludge and dirt that accumulates so that the fresh fluid would keep the plunger in the solenoid from sticking. If you do not know the exact recommended transmission intervals of your car, it is better to check with the owner’s manual.