How to Solve P0720: Torque Converter/Brake Switch B Circuit Low

When your car’s check engine light illuminates, it’s important not to ignore it. One of the error codes you might encounter is the P0720 code, which refers to the Torque Converter/Brake Switch B Circuit Low. In this article, we will explore what this error code means, its symptoms, possible causes, and provide you with a step-by-step guide to solving it.

Whether you’re a car enthusiast or a DIYer, this article will help you address the issue and get your car back on the road.

1. Introduction

Modern cars are equipped with advanced diagnostic systems that can detect and report any issues that arise. The P0720 error code indicates a problem with the Torque Converter/Brake Switch B Circuit Low. Understanding this code and knowing how to troubleshoot it can save you time and money by avoiding unnecessary visits to the mechanic.

2. Understanding the P0720 Error Code

The P0720 error code specifically points to an issue in the Torque Converter/Brake Switch B Circuit. The torque converter is a critical component of an automatic transmission system, responsible for transferring power from the engine to the transmission. The brake switch, on the other hand, detects when the brake pedal is engaged and signals the transmission to disengage the torque converter lock-up clutch.

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3. Symptoms of P0720 Error Code

When the P0720 error code is triggered, you may experience the following symptoms:

  • Illumination of the check engine light on the dashboard
  • Harsh shifting or failure to shift gears smoothly
  • Decreased fuel efficiency
  • Loss of power or sluggish acceleration
  • Overheating transmission

If you notice any of these symptoms, it’s important to address the issue promptly to avoid further damage to your vehicle.

4. Causes of P0720 Error Code

The P0720 error code can be caused by various factors, including:

  • Low transmission fluid level
  • Faulty wiring or connectors in the Torque Converter/Brake Switch B Circuit
  • Malfunctioning torque converter clutch solenoid
  • Defective brake switch
  • Problems with the transmission control module (TCM)

Now that we understand the code and its possible causes, let’s proceed with the step-by-step guide to solving the P0720 error code.

5. Step-by-Step Guide to Solve P0720 Error Code

Step 1: Check the Transmission Fluid Level

Start by checking the transmission fluid level. Low fluid levels can cause erratic behavior in the transmission and trigger error codes. Locate the transmission dipstick, usually labeled and located near the engine bay, and ensure the fluid level is within the recommended range. If the fluid is low, top it up using the manufacturer’s recommended fluid type.

Step 2: Inspect the Wiring and Connectors

Next, carefully inspect the wiring and connectors associated with the Torque Converter/Brake Switch B Circuit. Look for any visible signs of damage, corrosion, or loose connections. Ensure that all wires are securely connected and free from debris. If you identify any issues, repair or replace the affected components accordingly.

Step 3: Test the Torque Converter Clutch Solenoid

The torque converter clutch solenoid plays a crucial role in the operation of the torque converter. To test its functionality, you may need a multimeter. Consult your vehicle’s service manual to locate the solenoid and follow the specified testing procedure. If the solenoid fails the test, it may need to be replaced.

Step 4: Check the Brake Switch

The brake switch is responsible for signaling the transmission to disengage the torque converter lock-up clutch when the brake pedal is pressed. Inspect the brake switch for any signs of damage or wear. Test the switch using a multimeter to ensure it is functioning correctly. If necessary, replace the brake switch to resolve the error code.

Step 5: Inspect the Transmission Control Module (TCM)

Lastly, if the issue persists, it’s advisable to inspect the transmission control module (TCM). The TCM is responsible for controlling various aspects of the transmission system. It’s important to ensure that it is functioning correctly and not causing the error code. If you suspect a faulty TCM, it’s best to consult a professional mechanic for further diagnostics and repair.

6. Tips for DIY Troubleshooting

  • Always consult your vehicle’s service manual for specific instructions and diagrams related to your car’s make and model.
  • Take necessary safety precautions, such as disconnecting the battery before working on electrical components.
  • Keep a record of the steps you’ve taken and the parts you’ve inspected or replaced for future reference.
  • If you’re unsure or uncomfortable performing any of the troubleshooting steps, it’s recommended to consult a qualified mechanic.

7. Conclusion

The P0720 error code related to the Torque Converter/Brake Switch B Circuit Low can be resolved with careful troubleshooting and diagnosis. By following the step-by-step guide provided in this article, you can effectively address the issue and potentially save money on costly repairs. Remember to stay safe, refer to your vehicle’s service manual, and don’t hesitate to seek professional assistance if needed.


1. Can I continue driving my car with the P0720 error code?

It is generally not recommended to drive your car with the P0720 error code, as it can lead to further damage to your transmission. It’s best to address the issue promptly to avoid any potential complications.

2. Can I clear the P0720 error code using an OBD-II scanner?

While you can clear the error code using an OBD-II scanner, it is important to note that simply clearing the code will not fix the underlying issue. It’s crucial to diagnose and resolve the cause of the error code to prevent it from reoccurring.

3. How much does it cost to fix the P0720 error code?

The cost of fixing the P0720 error code can vary depending on the cause of the issue and your location. DIY troubleshooting can save you money, but if you need to replace components or consult a professional mechanic, the cost may increase. It’s advisable to obtain quotes from local mechanics to get a more accurate estimate.