Operation and main failures of the transmission valve body

The automatic transmission has many parts that together form a complex system. In case there is a failure in one component, it can cause major breakdowns. Today we will tell you about the transmission valve body, what it is, how it works and what are the faults that occur most frequently.

What is a transmission valve body?

The transmission valve body is a very important element for the automatic transmission proper function. It is known as the automatic gearbox “brain”, since it is the control center of a kind of labyrinth made up of valves, solenoids and lines and is the transmission most complex component.

Transmission valve body's function is to divert the transmission fluid (ATF) required by the transmission's clutch and brake packs so that the vehicle changes gears according to driving conditions.

Based on the driving conditions of the vehicle and the information received from other components, such as sensors and the Transmission Control Unit is responsible for managing the operation of the solenoids and gear changes.

Components of a transmission valve body

The transmission valve body is made up of a set of valves and springs, which are located inside a metal body with ducts through which the ATF flows. In addition to solenoids that are electromagnetic actuators that direct the ATF through hydraulic pressure.

The components are divided into:

• Hydraulic block, which includes the valves, springs, filters, oil passages and balls.
• Electrohydraulic actuators or solenoids.
• Sensors: temperature, speed and pressure.
• Electrical wiring.

For proper operation, the valve box needs the Engine Control Unit (TCU) or ECU, a computer designed to control mechanical components such as the gearbox.

The ECU (TCU), performs calculations based on the information received by other ECUs, vehicle control units or sensors, so that it can recognize driving conditions in real time, and adapt the behavior of the gearbox through the valve body.

What are the types of transmission valve body?

There are two main types of valve body: electronic valve and hydraulic valve.

• Electronic valve body. The electronic valve uses the transmission's ECT electronic system as a control to operate all shifts. Late model cars use the ECT electronic system as the main control to operate the shifts in the automatic transmission, and some models have bands and clutches that are operated through the hydraulic system. Electric valves are used in the hydraulic circuits so that the transmission has more elaborate and advanced control schemes than transmissions that are not electronically controlled.
• Hydraulic valve body. The other type of valve body is hydraulic, a system that works by using hydraulic pressure to control each valve linked to the gear lever. This system is responsible for upshifting from second to third gear.

Bad Transmission Valve Body Symptoms

• Incorrect gear change. The transmission valve body is the main control system for gear shifting at the correct rpm, so when there is any damage to this component, the vehicle will shift gears at the wrong times, you can see an increase in unexpected fuel consumption, gear hopping, or upshifting or downshifting.
• Slip transmission. Slippage can be caused by valves not extending as they should, or stuck inside the valve body, or cause the gears not to mesh correctly and slip as the throttle is lowered.
• Hitting or banging sounds. They can occur during gear changes, backing up, or when applying the brakes.
• Sudden gear changes. When a valve body is damaged the driver will feel forward jerking every time they change gear.
• No gear changing. This can occur while driving as the driver speeds up or slows down.
• Transmission fluid leak. This is one of the most serious symptoms, which can cause overheating in the transmission since the ATF has the function of lubricating the parts of the system and preventing the temperature from increasing. A damaged valve body can cause fluid to leak because it can flow in the wrong places.
• You cannot downshift. One of the most obvious symptoms of valve body damage is an inability to downshift due to incorrect ATF displacement causing the vehicle not to pressurize the gears in order to slow down.
• Check engine light. In the event of one of these failures, the check engine light will come on and when taking the vehicle to a mechanic with an OBD2 scanner, they will find one of the valve body related error codes such as P2707, P0829, P0783, P0751 and P0715.
• Delayed garage shifts. It consists of a delay of two or more seconds, or an abrupt change when changing the lever from “Parking” to “Drive” or “Reverse”, which is known as “garage shifts”. Sometimes this situation only occurs in one scenario, for example, when changing from park to reverse, so drivers try to limit the number of times they perform these maneuvers.

Can you drive with a faulty transmission valve body?

At first, the symptoms of an automatic transmission failure may be easy to ignore because they don't seem serious, but they become more apparent with continued driving because they can lead to overheating, safety hazards, and costly repair failures.
If you notice any of the above symptoms, take your vehicle to a mechanic to avoid a more serious problem.

Replace or rebuild, which option to choose?

If you are wondering “What is the cost of a transmission valve body replacement and rebuild?” the simple answer is that a failure of this part is not cheap. According to the AAA (American Automobile Association), the cost to replace the transmission valve varies between $300 and $1,000, depending on the vehicle´s year, model and brand.

The transmission valve body can also be rebuilt at a specialized repair shop, or you can purchase this remanufactured part to save a significant amount of money.

Tips for maintaining a transmission valve body

Maintaining the vehicle according to the manufacturer's recommendations, keeping an eye on the transmission fluid level, choosing the right ATF for the vehicle, and driving correctly are the best recommendations for a healthy automatic transmission system.

If you notice one of the symptoms mentioned in this post, or the check engine light comes on, see your mechanic before the problem becomes more serious. In Sun Transmissions you will find the spare parts for automatic transmission that you can purchase through our online store, like automatic transmission fluid, automatic transmission additives, automatic transmission sensor, and much more. You can find power steering parts too. Browse our online store and if you have questions we will gladly assist you through the online chat or contact form.