So, what is a transmission valve body? How does it work? What are some of the symptoms of a faulty one?
Both manual and automatic gearboxes have developed vastly over the years. What once needed incredible hand-to-eye coordination and a great deal of patience to operate, can now be done as easily as breathing in and out.
While it’s true that manual gearboxes, on the whole, have become a lot smoother and easier to control, giving drivers of modern cars a much better quality of drive. The real improvement has come in the form of the automatic gearbox.
When they were first introduced to the market, the idea of not having to change gear was a lot better than the product we were given. The early automatic boxes felt slow, lethargic and only contained a very small amount of gears, which made them feel incredibly restricted.
Since then however, technology has made huge strides in making our gear changing effortless. This is mainly down to the additions to the automatic box itself. Such components as; synchronisers, planetary gears and valve bodies, have allowed for much smoother gear changing as well as better fuel economy. The modern gearbox is highly complex and technical, usually requiring specialists to both diagnose and fix faults.
Valve Body Function
Your valve body is truly the brains behind the operation however when it comes to automatic gear changing. This ingenious component is made up of a large number of valves and galleries that are used to control gear change so that you, as the driver, don’t have to.
These valve bodies are either controlled electronically or via hydraulics that uses transmission oil.
Either way, if you suspect you have a faulty valve body, read on and we’ll do our best to help.
A bad valve body can cause a lot of problems with your automatic transmission. Below we‘ve put together a list for you of the top 6 symptoms of a bad valve body; some of these will apply only to electronic valves, some will only apply to a hydraulic system, and some will overlap between the two.
Symptoms of a Bad Valve Body
- Wrong gear shifting
- Slipping transmission
- Not Changing Gears When it Should
- Sharp gear changes
- Transmission fluid leaks
- Harsh Noises When Changing Gear
With that in, here’s our more detailed list of 6 symptoms of a faulty valve body.
Wrong Gear Changes
As stated in the introduction, your valve body will be the brains behind your gear change on an automatic gearbox. They are designed to not only respond to your throttle pedal but have also been created to change gear at the most economical RPM to help make your vehicle as fuel-efficient as possible.
So, if you notice that your vehicle’s recently decided to either change up or down a gear when you were expecting the opposite, this could be a sign of a faulty valve body. Also, if you notice that your gearbox is skipping gears when shifting either up or down, this could also point towards a faulty valve body.
Most of you will know the feeling of having your clutch slip whilst driving a manual box. But, maybe you’ve never experienced this while driving an automatic gearbox. The feeling is quite similar; as you lower the throttle pedal to accelerate, your RPM increases, but your speed doesn’t.
90% of the time, this would indicate a worn-out friction plate that needs replacing on a manual box. However, on an automatic box, it’s not quite that simple. You see, it could be that a valve inside the valve body assembly has started sticking or is no longer fully extending as it should. This could prevent gears from being fully engaged, causing them to slip as you take up the drive.
Not Changing Gears When it Should
Similar to the “wrong gear change” section, if your vehicle isn’t changing gears when it should be, this could indicate that your valve body is at fault. This kind of fault is usually most noticeable if you’ve driven or you’ve owned the car for many years and have gotten to know how it drives on a day to day basis. You know roughly when a gear change should take place as you accelerate, and at what rate your vehicle shifts down the gears as you slow down.
If you begin to notice that your vehicle has a delay between changing gears via an increase in RPM when both accelerating or decelerating before changing gears, then once again, this would suggest that your valve body is delaying the gear change and will require some diagnosis to find out why.
Sharp Gear Changes
As well as not changing gears when it should, you might also notice that your vehicle is slowly becoming a lot harsher in how it shifts up and down gears.
By design, nearly all modern automatic gearboxes should be smooth when changing gears to improve drive quality and driver comfort. However, if your valve body is faulty, this can cause a much sharper gear change, usually felt by the driver. Instead of smoothly disengaging from one gear and gently engaging the new gear, you may find that your vehicle “snatches” at new gears, causing the car to jerk forwards as it does so.
If this is happening to you, try to get your vehicle looked at and repaired as soon as possible as this kind of faulty will only usually get worse and cause more damage as it does so to other gearbox components and mounts.
Harsh Noises When Changing Gear
This fault is pretty straight forward. Just as if you were driving a manual gearbox and heard harsh noises when changing gear, this would point towards a faulty gearbox; the same is often true with an automatic box.
This is usually caused by the valve body not waiting to disengage a gear while engaging a new one. It’s like putting a screwdriver into the propellers of a turning fan. This is what gives you the harsh grinding noise.
With this in mind, get it looked at and repaired ASAP as you run the risk of having your valve body ruin the gears within your gearbox.
Transmission Fluid Leak
A fluid leak will, of course, only be noticeable on a hydraulic valve body system. These hydraulic systems work by having fluid pushed and pulled around various galleries to engage or disengage certain valves. This system is great and works well as the oil will keep the galleries lubricated and prevent excessive heat build-up.
There’s usually only ever a problem when your gearbox develops an oil leak, and there’s no longer enough oil to operate your valves effectively. A regular inspection under your vehicle (provided there is no undertray) to check for leaks can be a very effective way of catching an oil leak early on.
If you spot a leak, get it fixed as soon as possible as the cost for repairing a valve body oil leak is much cheaper than replacing an entire valve body because it’s been run dry.
Valve Body Location
The valve body is usually located inside your automatic transmission case, towards the lower side of the box. You will often see it when you remove the transmission pan.
They’re often submerged in transmission fluid and can vary in size depending on the size of the gearbox. Some will sit outside of the gearbox but most are housed inside and will require you to remove the transmission pan in order to change the valve body.
Valve Body Replacement Cost
A valve body costs 200$ to 1000$ for the part and a 200$ to 500$ in labor cost. You can expect a total replacement cost of 400$ to 1500$ for a valve body replacement.
As with most automatic gearbox components, these units aren’t cheap to replace as the work often has to be carried out by someone who specializes in such work. It could be more viable for you to have your current valve block repaired if the fault allows you to.
Either way, the best way to save your pennies is to stop driving the vehicle as soon as you suspect a fault and to get it looked at straight away, as this will prevent further damage to other components.
So, there we have it. While automatic transmission faults are fairly uncommon these days, it would be wrong to say they never happen. Due to the relatively low numbers of automatic gearbox faults, it can be difficult to find help when it happens to you. So, hopefully this guide can serve you well if you find yourself in this situation.
We would always recommend getting your vehicle properly diagnosed if you suspect that your transmission is faulty, as leaving it to develop will not only be dangerous for you as the driver, but you’ll also run the risk of damaging other engine and gearbox components unnecessarily.
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Founder, owner & main author of Mechanic Base. I have been repairing cars for more than 10 years, specialized in advanced diagnostics & troubleshooting. I have also been a drifting driver and mechanic for over 7 years.