Generator Control Circuit Malfunction (P0620 Code Troubleshooting)

generator control circuit malfunction

If you’ve encountered the dreaded P0620 code, you’re likely facing a malfunction in the generator control circuit of your vehicle.

This generic powertrain code, also known as “Alternator Control Circuit Malfunction,” is stored when the PCM (Powertrain Control Module) detects an issue in the circuits responsible for controlling and regulating the output current of the alternator.

While diagnosing and repairing this code can be complex, this comprehensive guide will provide you with the necessary information to troubleshoot and resolve the P0620 code effectively.

Understanding the P0620 Code

The alternator plays a crucial role in your vehicle’s electrical system, supplying power to various components and charging the battery.

The control module, often incorporated into the PCM, oversees the operation and output of the alternator.

It precisely regulates the alternator to generate the required current based on the vehicle’s power demands, optimizing fuel efficiency and component longevity.

However, if a failure or malfunction occurs in any circuit or component involved in controlling the alternator, it can disrupt the power supply to different control modules, affecting the overall functioning of your vehicle.

The P0620 code is triggered when the PCM or another affected control module detects a fault in the circuits responsible for controlling or regulating the alternator’s output current.

Common Causes of the P0620 Code

To effectively diagnose and resolve the P0620 code, it’s important to understand the common causes behind this malfunction.

While the specific causes may vary depending on your vehicle make and model, the following are some potential culprits:

  1. Defective Alternator: A faulty alternator can lead to irregular output current, triggering the P0620 code. Insufficient charging or overcharging of the battery can result from a malfunctioning alternator.
  2. Defective Alternator Control Module: The control module responsible for regulating the alternator’s operation may experience internal faults or programming errors, leading to the P0620 code.
  3. Wiring Issues: Damaged, burnt, shorted, disconnected, or corroded wiring and connectors within the alternator control circuit can disrupt the flow of electrical signals and trigger the P0620 code.
  4. Voltage Spikes: Improper jump starting procedures or voltage spikes can occur during battery replacement or electrical system repairs. These voltage spikes can damage control modules, including the PCM and alternator control module, leading to the P0620 code.
  5. Battery Defects: Internal short circuits or other defects within the battery can cause damage to control modules, including the PCM and alternator control module, resulting in the P0620 code.

Symptoms of the P0620 Code

When the P0620 code is present, you may experience various symptoms indicating a malfunction in the generator control circuit.

While the specific symptoms can vary depending on your vehicle, some common indicators of the P0620 code include:

  1. Illuminated Warning Light: The check engine light or battery/charging light may illuminate on the dashboard, signaling a detected fault in the generator control circuit.
  2. Additional Trouble Codes: Along with the P0620 code, other related trouble codes may be stored in the PCM. These codes can provide further insight into the specific areas of concern within the electrical system.
  3. Abnormal System Voltages: The electrical system may exhibit abnormally high or low voltages, affecting the performance of various components and systems.
  4. Battery Damage: Depending on the nature of the malfunction, the battery may suffer damage or experience irregular charging, leading to diminished performance and potential starting or power supply issues.

Diagnosing the P0620 Code

To pinpoint the exact cause of the P0620 code, a systematic diagnostic process is required.

While professional diagnostic equipment and expertise are recommended for thorough diagnosis, here are some general steps to help you get started:

  1. Scan for Trouble Codes: Use an OBD-II scanner to retrieve all stored trouble codes, including the P0620 code. Write down the codes and freeze frame data for reference during the diagnostic process.
  2. Inspect Alternator and Wiring: Check the alternator for any signs of physical damage or loose connections. Inspect the wiring and connectors within the alternator control circuit for any visible issues such as frayed wires, corrosion, or loose connections.
  3. Test Voltage Output: Using a digital volt/ohmmeter (DVOM), measure the voltage output of the alternator. Compare the readings to the manufacturer’s specifications to determine if the alternator is functioning within the expected range.
  4. Check Fuses and Relays: Inspect the fuses and relays related to the generator control circuit for any signs of damage or failure. Replace any faulty components as necessary.
  5. Evaluate Control Module Ground: Ensure that the control module has a proper ground connection. Check for corrosion or loose connections that may impede the flow of electrical signals.
  6. Consult Technical Service Bulletins (TSBs): Research any relevant TSBs that pertain to your specific vehicle make, model, and year. These bulletins may provide additional diagnostic and repair information specific to known issues related to the P0620 code.
  7. Clear Codes and Test Drive: After addressing any visible issues and conducting necessary repairs, clear the codes from the PCM. Take the vehicle for a test drive to monitor if the P0620 code reappears. If the code persists, further diagnosis may be required.

Note: Due to the complexity of the CAN bus system and the specific diagnostic requirements of individual vehicles, professional assistance may be necessary to diagnose and repair the P0620 code accurately.

Repairing the P0620 Code

Once the root cause of the P0620 code has been identified, you can proceed with the appropriate repairs. The following are potential repair options depending on the specific diagnosis:

  1. Alternator Replacement: If the alternator is determined to be defective or not functioning within the manufacturer’s specifications, replacing it with a new or remanufactured alternator may be necessary.
  2. Alternator Control Module Replacement: In cases where the alternator control module is found to be faulty, replacing it with a new module or reprogramming the existing module may be required.
  3. Wiring Repair or Replacement: Repair or replace any damaged, burnt, shorted, disconnected, or corroded wiring and connectors within the generator control circuit.
  4. PCM Replacement: In rare cases, if the PCM is determined to be at fault and all other potential causes have been addressed, replacing the PCM and reprogramming it may be necessary.

Note: It is essential to follow vehicle-specific repair procedures outlined in the manufacturer’s service manual or consult with a qualified technician when performing repairs related to the P0620 code.

Importance of Resolving the P0620 Code

While the P0620 code may initially seem like a minor issue due to the lack of noticeable symptoms, it is crucial to address this code promptly.

The generator control circuit plays a crucial role in charging the battery and supplying power to various electrical components.

Ignoring the P0620 code can lead to potential drivability issues, stalling when idling, and even more severe electrical system malfunctions.

By resolving the P0620 code and ensuring the proper functioning of the generator control circuit, you can maintain the overall performance and reliability of your vehicle’s electrical system.

P0620 Generator Control Circuit Malfunction >> Check out the video below:


Dealing with the P0620 code can be challenging, given the complexities involved in diagnosing and repairing the generator control circuit malfunction.

However, armed with the knowledge and understanding provided in this guide, you can approach the troubleshooting process with confidence. Remember to consult the manufacturer’s service manual or seek professional assistance when necessary to ensure accurate diagnosis and resolution of the P0620 code.

By promptly addressing the underlying issues, you can restore your vehicle’s electrical system to optimal functioning and enjoy a reliable driving experience.

Steve P.

Steve is an automotive technician, technical writer, and Managing Editor. He has held a lifelong passion for cars, with a particular interest in cars like the Buick Riviera. Steve is based in Boise, Idaho.

Recent Posts

error: Content is protected !!