Troubleshooting the P0620 Trouble Code – Control Module VSS Output “B” Malfunction

If you own a vehicle and suddenly encounter the P0620 trouble code, don’t panic. The P0620 code refers to a control module VSS output “B” malfunction. This issue can affect your vehicle’s performance, but with the right knowledge and a little bit of DIY spirit, you can resolve it on your own. In this article, we will guide you through the process of troubleshooting and fixing the control module VSS output “B” malfunction, helping you get your car back in top shape.


The control module VSS output “B” malfunction, indicated by the P0620 trouble code, occurs when the powertrain control module (PCM) detects a problem with the vehicle speed sensor (VSS) output signal. This signal is crucial for various systems within your vehicle, including the transmission, cruise control, and speedometer. When the control module detects an issue with the VSS output, it triggers the P0620 trouble code.

Understanding the P0620 Trouble Code

The P0620 trouble code can occur in different vehicle makes and models, and it is essential to understand its implications. When this code is triggered, it signifies a problem with the control module’s VSS output “B.” The control module relies on the VSS output to regulate various functions and systems in your vehicle. When the VSS output malfunctions, it can affect the transmission shifting, speedometer accuracy, and cruise control operation.

Symptoms of a Control Module VSS Output “B” Malfunction

When the control module VSS output “B” malfunctions, several symptoms may manifest. These symptoms can vary depending on the vehicle make and model, but some common signs include:

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  1. Check Engine Light: The illumination of the check engine light is a common indicator of a trouble code, including the P0620 code.
  2. Inaccurate Speedometer: You may notice that your speedometer behaves erratically or provides inaccurate readings.
  3. Transmission Issues: The malfunctioning VSS output can affect the transmission shifting, causing rough or delayed gear changes.
  4. Cruise Control Problems: If your vehicle has cruise control, it may fail to engage or maintain a steady speed due to the control module VSS output malfunction.
  5. Loss of Power: In some cases, the engine may experience a loss of power or reduced performance.

Causes of the P0620 Trouble Code

To effectively troubleshoot the P0620 trouble code, it is crucial to understand the potential causes. Some common causes include:

  1. Faulty Control Module: A malfunctioning control module can lead to the P0620 trouble code. This could be due to internal circuitry issues or a software malfunction.
  2. Defective Vehicle Speed Sensor: A faulty or failing vehicle speed sensor can disrupt the VSS output signal, triggering the P0620 code.
  3. Wiring or Connector Problems: Damaged or loose wiring connections can interfere with the VSS output, leading to the trouble code.
  4. Battery Voltage Issues: Insufficient voltage from the battery can affect the control module’s operation and trigger the P0620 trouble code.

Diagnosing the Control Module VSS Output “B” Malfunction

Before proceeding with the repairs, it is essential to diagnose the root cause of the P0620 trouble code. Follow these steps to identify and address the issue:

Step 1: Check the Battery

Start by inspecting the battery for any signs of damage or corrosion. Ensure that the battery connections are secure and clean. Low battery voltage can cause issues with the control module, leading to the P0620 trouble code.

Step 2: Inspect the Wiring and Connectors

Carefully examine the wiring harness and connectors associated with the control module and the vehicle speed sensor. Look for any signs of damage, frayed wires, or loose connections. Repair or replace any damaged components as necessary.

Step 3: Test the Control Module

Using a diagnostic scan tool, retrieve the trouble codes stored in the control module. Clear any existing codes and check if the P0620 code returns. If it does, further testing of the control module may be required. Consult your vehicle’s service manual or seek professional assistance.

Step 4: Check the Vehicle Speed Sensor

Inspect the vehicle speed sensor, located on the transmission or drivetrain. Ensure it is securely mounted and free from any debris or obstructions. Test the sensor’s output using a digital multimeter or consult a professional technician to perform the necessary tests.

Fixing the Control Module VSS Output “B” Malfunction

Once you have identified the cause of the P0620 trouble code, you can proceed with the necessary repairs. Keep in mind that working with the vehicle’s electrical system requires caution and, if you are unsure, it is advisable to seek professional assistance. However, if you’re confident in your DIY skills, follow these steps to fix the control module VSS output “B” malfunction:

Step 1: Replace the Control Module

If the control module is determined to be faulty, you will need to replace it. Consult your vehicle’s service manual or seek guidance from a reputable source to ensure you select the correct control module for your specific make and model. Disconnect the old control module, install the new one, and reconnect all wiring connections.

Step 2: Repair or Replace Faulty Wiring or Connectors

If the issue lies with damaged wiring or connectors, repair or replace them accordingly. Use appropriate tools and materials to ensure secure connections. Properly insulate any repaired wiring to avoid future issues.

Step 3: Replace the Vehicle Speed Sensor

In cases where the vehicle speed sensor is defective, it is necessary to replace it. Refer to your vehicle’s service manual or seek professional assistance to perform this task. Ensure the new sensor is compatible with your vehicle and properly calibrated.

Preventive Measures to Avoid the P0620 Trouble Code

To minimize the risk of encountering the P0620 trouble code in the future, consider implementing these preventive measures:

  1. Regular Maintenance: Adhere to your vehicle’s recommended maintenance schedule, including periodic inspections of the control module, wiring, and connectors.
  2. Battery Maintenance: Keep your vehicle’s battery in good condition by cleaning the terminals, checking the voltage regularly, and replacing it when necessary.
  3. Safe Driving Habits: Avoid harsh driving conditions and excessive speed, as they can put unnecessary strain on the control module and vehicle speed sensor.
  4. Quality Repairs: When replacing components related to the control module or vehicle speed sensor, choose high-quality parts from reputable manufacturers.


Dealing with the P0620 trouble code, indicating a control module VSS output “B” malfunction, can be challenging. However, armed with the knowledge and steps outlined in this article, you can diagnose and fix the issue yourself. Remember to approach the repairs with caution, prioritize safety, and seek professional assistance if needed. By taking proactive measures and performing regular maintenance, you can reduce the chances of encountering this trouble code in the future.


1. Can I continue driving my vehicle with the P0620 trouble code?

While it may be possible to drive the vehicle with the P0620 code, it is not recommended. The malfunctioning control module VSS output can affect important systems, such as the transmission and cruise control, compromising your vehicle’s performance and safety. It is best to address the issue promptly.

2. How much does it cost to replace a control module?

The cost of replacing a control module can vary depending on the make and model of your vehicle, as well as where you source the replacement part from. Additionally, labor costs for professional installation should be taken into account. It is advisable to consult a reputable mechanic or dealership for an accurate cost estimate.

3. Is it possible to repair a faulty vehicle speed sensor instead of replacing it?

In some cases, it may be possible to repair a faulty vehicle speed sensor, but this depends on the specific issue and the sensor’s design. However, considering the critical role of the vehicle speed sensor in various systems, it is generally recommended to replace it with a new, reliable component for optimal performance and longevity.