The P0740 code is one of the most serious trouble codes you will ever see. When your vehicle’s torque converter clutch circuit is not working properly, you will have difficulty shifting gears.
The solutions for the P0740 fault code are sometimes straightforward, simple, and affordable. In other cases, they are more important and expensive repairs.
While the symptoms present in your car can help guide you, a careful diagnosis is the only real way to determine what is wrong with your vehicle.
Torque Converter Operation
In modern vehicles with automatic transmissions, there is a torque converter between the transmission and the engine, which increases torque output and provides more power to the rear wheels.
There is a fluid coupling device inside the torque converter. This device is what actually connects the engine to the transmission. Multiplies the torque, equalizing the speeds.
The amount of hydraulic fluid in this coupling is controlled by the powertrain control module (PCM) through the transmission control module (TCM).
If the TCM detects a fault within the torque converter circuit, fault code P0740 is activated. While this is a generic powertrain code applicable to all vehicle types, the specific solution may vary depending on your transmission.
Transmission construction style varies from manufacturer to manufacturer. Some use a TCC solenoid connected to the transmission case using wires and plugs.
In other cases, the TCM bolts directly to the transmission case or maybe a single unit. These style differences are one of the reasons you should look for specific repairs related to your vehicle.
You may also be interested in Code P0743. Causes, Symptoms and How to Fix It
What is the P0740 code?
The presence of a P0740 code It means that the ECU has detected a problem in the circuit that controls the torque converter clutch solenoid.
A malfunction of the torque converter clutch (TCC) circuit is what triggers the P0740 trouble code. All vehicles manufactured since 1996, regardless of make and model, may return this generic trouble code.
However, different models may have different steps for repairs and diagnosis.
The transmission control module (TCM) controls the torque converter clutch (TCC). When disengaged, the TCC locks the converter housing to the turbine shaft, creating a 1-to-1 connection between the transmission and engine to prevent slippage.
If the clutch application is abnormal, trouble code P0470 appears.
What Are the Symptoms of Code P0740?
You will experience one or more of the following symptoms if you have activated the code P0740 in your car.
- Activation of the Check Engine light
- Increased fuel consumption.
- The transmission does not shift gears correctly.
- The changes are made abruptly.
- The engine shuts off when changing gears.
- Transmission overheating.
- Engine stall.
- The transmission shudders or shakes when stopping or accelerating.
- The vehicle does not move when in motion.
What Are The Causes Of Code P0740?
There are many probable causes for the appearance of the P0740 fault code. Some of the most common are presented below:
- Defective torque converter solenoid.
- Defective torque converter.
- Damage, short circuits, or loose connections in the wiring harness.
- Faulty engine coolant temperature sensor.
- Defective valve body.
- Old, dirty, or too low transmission fluid.
- Dirty or damaged transmission fluid filter.
- A problem with the TCM or PCM.
- Internal pressure problem.
- Problem with the valve body.
How Serious Is Code P0740?
Fault code P0740 It can be serious, especially if you experience symptoms that affect your ability to drive. In some cases, your vehicle will stop or refuse to start when this code is activated, leaving you stranded.
Additionally, you can cause damage to the transmission if you continue driving in these conditions. Transmission repair can be very expensive, which is something you should avoid if possible.
Our recommendation is that, when you detect the P0740 code, you stop driving the car and immediately take it for diagnosis and repair.
How to Diagnose Code P0740?
Let’s see the steps necessary to carry out a good diagnosis of the fault related to code P0740.
- OBD2 scan tool.
- Digital multimeter.
1. Connect the scanner to the vehicle
- Scan your vehicle with the OBD2 scan tool, checking for the P0740 code and looking for other codes. You may see other transmission DTCs, including P0741, P0742, P0743, P0744, P2769, or P2770.
- If you see multiple transmission trouble codes, this likely indicates a fault in the electrical system.
- Clear all codes and perform a power-on test to see if the codes come back again.
2. Check the transmission fluid
- Check the transmission fluid. It should be bright and clear, typically a vibrant red. If it is brown, black, cloudy, or has visible debris floating in it, you should replace it.
- Change the filter as well and flush the system.
- Refill the system with new transmission fluid, making sure it is completely full.
3. Check the wiring
- Inspect the transmission wiring harness. Replace any damaged cables you see. The wiring diagram in your manual will be especially helpful in determining if all connections have been made safely.
- Reconnect any loose or disconnected wires you see and make sure the connections are not corroded.
- Use a digital multimeter to check the continuity of the transmission’s internal wiring. Touch the positive and negative leads of the multimeter to the appropriate pins on the TCC solenoid.
4. Check the TCC solenoid
- After removing the plug from the transmission harness, check the wiring in the transmission case and the torque converter clutch solenoid resistors.
- Depending on the make and model of your vehicle, the internal harness and solenoid may be one unit.
- Place the negative and positive leads of your multimeter, set on the ohm scale, to the appropriate pins of the TCC control circuit and power.
- The resistance must be within the specifications established by the manufacturer.
- If possible, inspect the TCC solenoid inside the transmission by removing the transmission oil pan if you get a reading that is OL or very high.
5. Check the torque converter
- If the code still is not clear, test the function of the clutch and torque converter.
- If these repairs don’t clear the code, you may have a more serious problem.
- In some cases, the transmission itself may need rebuilding. Other times, it could be a problem with the PCM or TCM.
- Either way, this is not a repair you should do at home. Take your car to a mechanic for further diagnosis.
6. Check the TCM
To determine what the actual feedback is in the TCM and if it is commanding the solenoid, you should keep track of the TCM with a scan tool, as TCC only activates under specific driving conditions.
To achieve comfortable TCC coupling, the solenoid is normally controlled by the duty cycle.
Digital storage oscilloscopes or graphic multimeters set to duty cycle will be needed to check if the TCM is actually sending a signal.
The negative connects to a good ground and the positive connects to the wiring harness that is plugged into the TCM. The TCM may fail when the cycle is intermittent or at 0 percent or 100 percent.
Common Errors When Diagnosing Code P0740
Do not assume that the torque converter is damaged when this code is activated. There are several causes for this code, including simple solutions like disconnected wires or the need for more transmission fluid.
Perform a thorough diagnosis before replacing expensive components.
How to Repair Code P0740?
There are several fixes that could address the P0740 fault code, including:
- Installing a new transmission.
- Perform a transmission check.
- Replace the TCM.
- Replace the transmission fluid filter.
- Replace the transmission fluid.
- Replace the torque converter.
- Replace the torque converter clutch solenoid.
- Replace the damaged wiring harness.
Is Code P0740 Serious?
A P0740 fault code It means that the ECU does not have full control of the torque converter, so you are sure to have drivability problems.
Located between the transmission and the engine, the torque converter works to match speed by multiplying torque to optimize vehicle performance. This increases fuel efficiency and reduces transmission fluid temperature.
If this element has problems in its operation, it will greatly affect the work of the transmission and the performance of the engine. In some cases, it even completely disables the engine. It is one of the most serious faults that your car can have.
Tips to Avoid Code P0740
Proper maintenance of the transmission system is the best way to avoid the code P0740 and other transmission-related trouble codes.
Check your transmission fluid regularly, and refill or replace it as necessary.
Transmission fluid that is dirty or too low can cause a number of transmission problems, some of which are relatively expensive to repair.
You will save a lot of time and money by staying on top of its regular maintenance.
You may also be interested in Error Code P0748 OBD – Electrical Pressure Control Solenoid
Transmission flushing or replacement is a good start to correct this error code. Of course, it must be accompanied by a complete circuit check of both the sensors and solenoids.
If any of these components are faulty, it could be the start of a bigger problem. Prolonged driving with this error code can cause the transmission fluid to overheat, which can cause more serious transmission problems.
It will be much more expensive for you to drive in these conditions. It is recommended that you stop the car and take it to a specialized service where they can diagnose and repair the fault.
If you want to know other articles similar to Code P0740. Causes, Symptoms, Diagnosis, and Repair you can visit the category Fault Codes.