It can be hard to figure out what the P0740 fault number means, at least when it comes to transmissions. What’s worse is that it’s pretty pricey to fix no matter what causes it. It’s so hard to figure out, though, that most repair shops, even transmission repair shops, will just tell you to buy a new transmission. They’re afraid they’ll get it wrong and have to pay for it.
If the fault number P0740 shows up, it means that the torque converter clutch circuit is open. It’s more likely that a bad torque converter clutch switch, a bad regulator valve, or a worn-out clutch is to blame. P0740 can also appears by low transmission oil or a broken torque converter.
What Does the P0740 Code Mean?
The torque converter clutch circuit fault is what the P0740 fault number really means. That clutch pack in the back of the transmission has nothing to do with the torque converter clutch. The clutch pack does the same thing that a clutch does in a car with a manual gear. The torque converter clutch (TCC) locks the engine with the torque converter in place. That is, to make the torque converter spin at the same speed as the engine.
Power is sent from the engine to the transmission through transmission fluid by the torque converter. To put it another way, there is no real link between the two. That’s needed for those kinds of communication, but it’s not very efficient. A lot of fuel and horsepower are wasted. Then, carmakers add a lock-up clutch, which makes the engine and transmission physically touch each other to improve economy.
The TCC, or lock-up, is only used when you’re just driving or not pressing down on the gas pedal very hard. In that case, locking up the torque converter doesn’t affect how well the car drives, and it also lowers the amount of fuel used and pollution released. It’s an easy trick that really works. Of course, it adds a lot of extra moving parts that make gearbox problems more likely.
The P0740 Code: How to Figure It Out
You may need a multimeter and a live data OBD2 reader to figure out what a P0740 fault code means. With the OBD2 live scan, you can check the TCC status and see how the torque converter RPMs compare to the engine RPMs while you’re moving. Once you have all the information in front of you, you can start driving and reach your favorite speed. As you keep the speed steady, you should see the TCC state change and the RPMs of the engine and torque converter match up.
If the TCC status doesn’t change, you can use a multimeter to test the TCC solenoid on a bench once it’s been taken off to make sure you made the right conclusion. Even if the TCC switch works, the regulator valve could still be broken, so take it off and check it next.
Why the P0740 Code Shows Up and How to Fix It
1. Solenoid for torque converter clutch
A torque converter clutch solenoid is a pretty easy-to-understand device. In essence, it’s just an electric actuator. When the transmission control module pushes a plunger inside the TCC solenoid, it turns it on. After that, the plunger pushes the TCC regulator valve, which sends transmission oil to the TCC to turn it on.
The solenoid is turned off by the transmission control module. This makes the piston and the spring-loaded TCC regulator valve move back. That takes the pressure from the transmission fluid away from the TCC, which releases it. The transmission control unit doesn’t know that the TCC is active when the TCC solenoid fails. That causes a P0740 trouble code to appear right away, along with maybe others in the same group.
This part of the TCC changes the TCC state on both the live data scanner and the transmission control module. With a live data scanner, that makes the problem clear, but a lab test is needed to be sure.
How to Fix and How Much It Will Cost
To fix a TCC solenoid, you have to replace it, which is generally pretty simple and faster than fixing most of the issues in this article. You can change the TCC switch without taking the valve body off because it sits on the side of it. You only need to take off the transmission oil pan and any metal plates that might be on top of the valve body. Then you take the solenoid’s plug out and the one or two bolts that are keeping it in place.
After putting everything together, you just add more transmission fluid and that’s it. It can cost anywhere from $50 to $150 for a new valve, but most people pay around $70. As for the work, you can expect to pay $150 to $200 for about 1.5 to 2 hours. That takes the average up to about $250.
2. Torque Converter Clutch That Is Worn Out
The torque converter clutch is the most important part of the TCC device. In terms of shape, the clutch is a lot like a friction plate on a regular manual gear. Since there is some slip every time it connects and disengages, it will wear out over time. It only slips for a short time, though, and it doesn’t happen nearly as often as it does in cars with manual transmissions. It also doesn’t feel that strong of forces.
So, in theory, the TCC clutch should easily last as long as the car does. And most of the time it does. But based on how you drive, the clutch may wear out before it should. The clutch may also break or come apart due to age or other problems with the transmission. The damage could happen at any point in the car’s life, but it usually happens after 120,000 miles.
How to Fix and How Much It Will Cost
The TCC clutch can’t be replaced by itself, which is a shame. It won’t even be for sale. You can either buy a new torque converter or have the one you already have fixed up. It can cost anywhere from $600 to several thousand dollars for a brand-new torque converter. It also costs several hundred dollars to rebuild a torque converter.
Then buying a torque converter that has already been fixed up is your best bet. At AutoZone, these torque converters cost about $200 to $300 and come with a guarantee that lasts for one year. You also get a core deposit of $30 to $65 that you can get back. This can sometimes bring the price down to $120. The work itself takes six to ten hours and costs between $600 and $1,000 at most repair shops. Adding everything up, the sum comes to about $1,000.
3. Not enough transmission fluid
This code (P0740) can mean that the transmission oil level is too low or is even bad. Transmission oil starts and stops shift solenoids. Through the TCC solenoid and valve control, it also use to turn TCC on and off. You can’t use the TCC if the transmission fluid level is low. This is because the TCC needs oil to work.
Transmission oil, old or burned out gets a lot softer or easier to squeeze. When this happens, the transmission fluid takes in all the movement of the shift solenoid and valve regulator. This keeps the TCC in place even when the TCC solenoid turns on. Check your owner’s manual to find out how to check the transmission fluid in your car. This is where you can find color charts for transmission oil online to check if it is stable.
4. Torque converter that is broken
The P0740 trouble code could also be caused by a torque converter that is faulty. The torque converter has the TCC built in. The pressure plate, the damper plate, and the contact plate are all inside. Another part is the turbine, which has a rotor and an impeller. There is a chance that the TCC won’t work right if any of these parts get broken.
If your torque converter isn’t working right, your gearbox might get too hot, make noises like grinding, slip, shift really hard, shake when you speed up, and other things. There is also a lot of high stop speed. It’s not easy to tell if a torque converter is broken, and you shouldn’t depend on symptoms alone.
If you think the gear converter is broken, have a professional look at the car. To replace the torque converter costs the same amount as to replace the TCC clutch, if it turns out to be broken. That means the usual cost, not including the cost of finding out what’s wrong, is $1,000 for labor and a remanufactured torque converter.
5. TCC Valves That Don’t Work Right
In a sense, the TCC regulator is an opening that diverts transmission fluid. It’s kind of like how shift solenoids work. The TCC regulator is a valve that changes the shape of the valve body and the way the TCC fluid lines are set up. The TCC solenoid moves the TCC regulator into place so that it lines up with the transmission fluid channels. Because of the pressure in the transmission fluid, that lets fluid go to the TCC and open it.
The regulator sleeve, regulator valve, and isolator valve are some of the working parts in the TCC regulator. It also has springs and O-rings. And all of these parts can break. Most of the time, the O-ring leaks. When the O-rings leak, the pressure of the transmission fluid inside the TCC valve drops. This means that the TCC doesn’t have enough force to engage.
If the sleeve, valve, springs, or something gets inside the transmission oil or breaks, it can also cause damage. The TCC valve will then lock up and become closed. The TCC solenoid won’t be able to move it, and based on the car, you’ll either see that the TCC isn’t working or that the torque converter RPMs don’t match when it is.
How to Fix and How Much It Will Cost
Once you have the TCC switch out, it’s pretty easy to check the TCC regulator. The movie at the top of this post shows you how to do that. The valve is generally held in place by a clip once the TCC solenoid is out. A magnet is use to pull the TCC regulator out after you pull the clip. You can look for damage to the O-rings, the valve body, or the springs once it’s out.
You can also see if the sleeve is jam. No matter what kind of damage you find, a new TCC regulator will cost you between $50 and $100. The work itself takes about an hour and a half to two hours and costs about $150 to $200. With parts and work, it costs about $200 all together.
This is how to take the TCC regulator off the valve body if you want to change it yourself.
Conclusion
It’s almost impossible to figure out what’s wrong with a P0740 without a live data OBD2 reader. I don’t think it will be easy even with one. Once it’s out, you’ll still need to use a voltmeter to test the TCC solenoid, look over the TCC regulator, and then put the torque converter back in if everything looks good. A TCC circuit is open is what the P0740 trouble code says, but that’s not usually what’s wrong.
It’s also important to note that P0740 often comes with other trouble codes that can help you figure out what might be wrong. Check the transmission fluid again before you work with the live data reader or take off the TCC solenoid. A P0740 trouble code can be caused by either not having enough transmission fluid or transmission fluid that has been oxidized. Just make sure you read your owner’s manual all the way through because the steps are different for each car.
