P0740: TCC Solenoid Circuit/Open Circuit Malfunction

What is P0740?

The diagnostic trouble code or DTC P0740 stands for “Torque Converter Clutch Solenoid Circuit/Open Circuit Malfunction.”

The error code basically means that the Powertrain Control Module (PCM) has caught some issue within the torque converter clutch (TCC) circuit (or torque converter clutch solenoid circuit).

The Powertrain Control Module uses the torque converter clutch to optimize car performance by lowering engine RPMs, reducing transmission fluid temperature, and improving fuel economy. If there’s any abnormality in the application of the torque converter clutch, the Powertrain Control Module will set off your check engine light (malfunction indicator lamp).

It’s important to note that many vehicle manufacturers don’t list P0740 as a possible code.

However, for the manufacturers that consider it a possible code, P0740 typically indicates that the control module (PCM or Transmission Control Module) senses an electrical fault with the torque converter clutch solenoid. It can also be an electrical fault with the solenoid’s circuit.

For some vehicles, the P0740 code is more telling of a mechanical problem with the transmission or torque converter.

How Does The Torque Converter Clutch Circuit Operate?

The TCC solenoid valve, an electrical device, is used with the torque converter clutch pulse width modulation (TCC PWM) solenoid valve to control TCC application and release.

The TCC solenoid valve connects to the transmission case assembly extending into the pump cover. This solenoid valve acquires ignition voltage via the Off/On/Crank voltage circuit.

The PCM regulates the solenoid by providing the ground path on the torque converter clutch solenoid valve control circuit. The PCM observes the throttle position sensor voltage, the vehicle speed, and other inputs — which helps it decide when to energize the TCC solenoid valve.

So when the PCM witnesses a continuous open, short to ground, or short to power in the TCC solenoid valve circuit, DTC P0740 is triggered. 

Common symptoms

You may first notice the check engine light (malfunction indicator lamp) illuminating. Apart from the engine light, here are some of the most common symptoms that your car may experience on detecting the P0740 code:

• Transmission won’t shift in or out of a particular gear
• Transmission overheats
• Limited transmission gear range
• Harsh transmission shifting
• Reduced fuel economy
• Increase in engine speed
• Car engine stalls
• A gear box warning light may appear
• Car shudders at certain speeds 

Can I still drive?

Not all check engine light codes mean danger in driving. However, code P0740 is serious because it can easily disrupt your normal driving experience.

Located between the transmission and the engine, the torque converter equalizes the engine speed by multiplying the torque to optimize vehicle performance. That means increasing fuel efficiency and reducing the transmission fluid temp.

But when the code P0740 is triggered, it implies that the PCM isn’t fully controlling the torque converter, causing drivability issues. You don’t want to be stuck at the 3rd or 4th gear forever.

So if you suspect or detect the DTC P0740, get the issue diagnosed and fixed as soon as possible. If you don’t, you risk getting stranded on the side of the road.

P0740 causes

This trouble code can be triggered for numerous reasons and can differ depending on whether your car is made by Volkswagen AG, Honda motor company, Mercedes, or any other manufacturer.

Here’s a quick list of the potential causes:

1. Transmission Fluid Issue:

• Incorrect transmission fluid level
• Internal transmission damage
• Low transmission fluid level
• Contaminated transmission fluid

2. Powertrain Control Module Issue:

• A faulty Powertrain Control Module
• Problem with the Powertrain Control Module, such as software that needs an update

3. Transmission Problem:

• Defective transmission converter clutch solenoid 
• Clogged transmission filter
• The torque converter clutch won’t engage or disengage
• Faulty sensor inhibiting proper torque converter clutch operation
• Issues with the transmission valve body
• Faulty torque converter clutch solenoid valve
• Irregular transmission maintenance
• A restriction within the transmission
• A faulty Transmission Control Module (TCM)

4. Wiring Issue:

• Faulty or corroded wiring to the torque converter clutch or TCC solenoid
• Open or shorted torque converter clutch solenoid valve harness or connector
• A torque converter clutch solenoid valve circuit has a poor electrical connection

5. Torque Converter Problem:

• A faulty torque converter clutch solenoid
• A damaged torque converter or clutch
• Electrical fault inside the TCC solenoid circuit

Diagnosis

Code P0740 can be caused by a faulty solenoid to a very pricey internal transmission problem. That’s why there isn’t a single fix for this code.

And since the diagnostic trouble code P0740 is severe, you should let a mechanic or transmission shop do a proper inspection and handle the repairs.

Here’s how a mechanic at a transmission shop will go about it:

Note: If there’s nothing wrong with the transmission fluid, your mechanic will follow a manufacturer-recommended diagnostic procedure to fix the issue. Remember that this diagnostic code may need removing or disassembling the transmission.

1. First, they’ll check if there are other DTCs. If any other codes exist apart from DTC P0740, they’ll thoroughly diagnose each before continuing with repairs.
2. Then they’ll check the transmission fluid for proper level and condition. If something looks odd, it may be the cause of the code P0740.
3. Once done, your mechanic will visually inspect the transmission wiring harness to look for signs of damage, fraying, or corrosion.
4. Then they’ll move on to check for continuity across the affected circuit. They do so using a multimeter set to the ohms scale. They’ll also use a factory-specific wiring diagram.
   The diagram will help them look for the appropriate pins corresponding to each end of the clutch solenoid circuit at their connection points with the transmission (internal harness) and transmission control module.
5. Then your mechanic will check for: a) Signs of a short-to-ground condition within the external portion of the harness, and b) Excessive resistance or open conditions within the internal harness or clutch solenoid.
6. Finally, they’ll locate the affected wiring harness or connector and repair it as necessary. In case continuity testing reveals that the issue lies within the transmission, your mechanic will extract the transmission oil pan in most automatic transmission cars.

After removing the transmission pan of an automatic transmission vehicle, they’ll conduct further testing of the clutch solenoid as specified by your particular vehicle’s manufacturer.

Note: Some codes related to P0740 include:

• P0741: Torque Converter Clutch Solenoid Circuit Performance/Stuck Off
• P0742: Torque Converter Clutch Circuit Stuck On
• P0743: Torque Converter Clutch Solenoid Circuit Electrical

Possible repairs for P0740 & Costs

Since the trouble code can be triggered due to multiple reasons, here’s a list of different repairs that your mechanic may perform to fix the P0740 code:

• Replacing the torque converter clutch or TCC solenoid
• Adding or replacing the transmission fluid and filter
• Repair faulty wiring to torque converter clutch (TCC) solenoid
• Repair connector plugs to the torque converter clutch solenoid
• Repairing or replacing the car’s existing transmission
• Replace the transmission control module (TCM)
• Replace the Powertrain Control Module

4 FAQS About P0740

Here are some FAQs related to P0740 and its affected parts:

1. What Are The Most Common P0740 Diagnosis Mistakes?

Whether you have a Volkswagen AG or a car by the Honda motor company, it’s common to assume that the torque converter needs to be replaced or rebuilt — when it could just be a faulty TCC solenoid or dirty transmission fluid.

Another common diagnostic mistake is believing the issue is caused by an engine misfire, a driveline, or an internal transmission problem.

The trick is to look at every aspect of each problem because it can reveal the correct solution quickly and efficiently.

2. What Is The Normal Operating Automatic Transmission Temperature?

The fluid temp in the automatic transmission would ideally range from 170-225 degrees Fahrenheit. If the transmission is slipping, the fluid temp could go above 240 degrees.

3. What Is A Valve Body?

A transmission valve body is an important component of an automatic transmission. It’s a maze-like control center made with valves, passageways, and solenoids that direct transmission fluid to where it’s required for gear changes.

So every time you move to the 2nd or 4th gear, you can thank the valve body.

4. Is CVT Fluid The Same As Automatic Transmission Fluid?

No, they aren’t.

CVT fluid is for vehicles utilizing a Continuously Variable Transmission (CVT) system, which has a different mechanism than Automatic Transmission systems. Automatic transmission fluid (ATF) has a different chemical composition than CVT fluid, so they’re not interchangeable.