P0620 Generator Control Circuit Malfunction
OBD2 Error Codes

P0620 Generator Control Circuit Malfunction

OBD-II Trouble Code P0620 - Datasheet

Generator control circuit malfunction.

Code P0620 is stored when the ECM detects a voltage other than what is expected.

What does trouble code P0620 mean?

This is a generic Diagnostic Trouble Code (DTC) applicable to many OBD-II vehicles (1996 and newer). This may include, but is not limited to, Hyundai, Mercedes-Benz, Buick, Ford, GMC, Chevrolet, Jeep, Cadillac, etc. Despite the general nature, the exact repair steps may vary depending on the model year, brand, transmission models and configurations.

A stored code P0620 means the powertrain control module (PCM) has detected a malfunction in the alternator control circuit.

The PCM normally supplies power and monitors the generator control circuit whenever the engine is running.

Each time the ignition is turned on and power is applied to the PCM, several controller self-tests are performed. In addition to performing a self-test on the internal controller, a Controller Area Network (CAN) is used to compare signals from each individual module to ensure that the various controllers are communicating as expected.

If a problem is detected while monitoring the alternator control circuit, a P0620 code will be stored and a malfunction indicator lamp (MIL) may illuminate. Depending on the perceived severity of the malfunction, multiple failure cycles may be required to illuminate the MIL.

Typical alternator: P0620 Generator Control Circuit Malfunction

What is the severity of the P0620 DTC?

Internal control module codes should always be taken seriously. A stored P0620 code can result in a variety of handling problems including no starting and / or low battery.

What are some of the symptoms of the code?

When code P0620 is stored, you should see the Check Engine light come on. Unfortunately, this is the only noticeable symptom associated with this code.

Symptoms of a P0620 trouble code may include:

  • Engine control problems
  • The engine stalls at idle speed
  • Delay in starting the engine (especially in cold weather)
  • Other stored codes

What are some of the common causes for the code?

Reasons for this code may include:

  • Defective PCM
  • PCM programming error
  • Open or short circuit in the generator control circuit
  • Unsuccessful generator assembly
  • Insufficient grounding of the control module
  • The voltage regulator is out of order
  • Generator is defective
  • Battery charge
  • The alternator circuit is suffering from poor electrical contact
  • Alternator harness open or shorted
  • PCM is faulty (this is the least likely cause)

What are some steps to troubleshoot the P0620?

Diagnosing the P0620 code requires a diagnostic scanner, battery / alternator tester, digital volt / ohmmeter (DVOM), and a reliable vehicle information source.

Search your vehicle information source for technical service bulletins (TSBs) that match the stored code, vehicle (year, make, model, and engine) and symptoms displayed. If you find the correct TSB, it can provide diagnostic information that will help you to a great extent.

Start by connecting the scanner to the vehicle's diagnostic port and retrieving all stored codes and freeze frame data. You will want to write this information down just in case the code turns out to be intermittent. After recording all relevant information, clear the codes and test drive the vehicle until the code is cleared or the PCM enters standby mode. If the PCM enters ready mode, the code is intermittent and harder to diagnose. The condition for which the P0620 was stored may even get worse before a diagnosis can be made. If the code is cleared, continue diagnostics.

Use a battery / alternator tester to check the battery and make sure it is sufficiently charged. If not, check the generator / generator. Follow the manufacturer's recommended specifications for minimum and maximum output voltage requirements for battery and alternator. If the alternator / generator does not charge, proceed to the next diagnostic step.

Use your vehicle information source to obtain connector views, connector pinouts, component locators, wiring diagrams, and diagnostic block diagrams relevant to the code and vehicle in question.

Check if there is battery voltage at the alternator / generator using the appropriate wiring diagram and DVOM. If not, check system fuses and relays and replace defective parts if necessary. If all fuses and relays are working properly, suspect that the generator / generator is faulty.

If the alternator is charging and the P0620 continues to reset, use the DVOM to test the fuses and relays on the controller power supply. Replace blown fuses if necessary. Fuses should be checked with a loaded circuit.

If all fuses and relays are working properly, a visual inspection of the wiring and harnesses associated with the controller should be performed. You will also want to check the chassis and motor ground connections. Use your vehicle information source to obtain grounding locations for associated circuits. Use DVOM to check ground integrity.

Visually inspect the system controllers for damage caused by water, heat, or collision. Any controller damaged, especially by water, is considered defective.

If the power and ground circuits of the controller are intact, suspect a faulty controller or a controller programming error. Replacing the controller will require reprogramming. In some cases, you can purchase reprogrammed controllers from the aftermarket. Other vehicles / controllers will require onboard reprogramming, which can only be done through a dealership or other qualified source.

  • Unlike most other codes, P0620 is likely caused by a faulty controller or a controller programming error.
  • Check the system ground for continuity by connecting the negative test lead of the DVOM to ground and the positive test lead to the battery voltage.

Common Mistakes When Diagnosing Code P0620

This problem can be tricky to diagnose correctly, so it's important that your mechanic doesn't immediately assume the PCM is at fault. To make sure it's not the PCM's fault, you need to clear the system and take a test drive to see if the code comes back.

Otherwise, a mechanic can unnecessarily replace your PCM - and pay you in the process - when something like the wiring is really to blame.

How serious is the P0620 code?

While this may seem like a minor issue because there are no noticeable symptoms, the P0620 code still needs to be addressed as soon as possible. Your car's power transmission and generator are essential to its overall functioning, and code P0620 can be the start of a much bigger problem if you don't address it right away.

What repairs can fix code P0620?

Your mechanic will likely need to do one of the following:

  • Replace any wires or other electronic components that don't work properly.
  • Replace or repair generator
  • Replace or repair PCM

Again, this last option is almost never needed.

Additional comments to consider regarding code P0620

The same issue that led to the code P0620 being stored could also be behind others. Just because they don't have a trouble code stored for them doesn't mean your mechanic shouldn't take the time to thoroughly inspect and make sure other parts of your car aren't suffering from abnormal voltage.

What is P0620 Engine Code [Quick Guide]

Need more help with the P0620 code?

If you still need help with DTC P0620, post a question in the comments below this article.

NOTE. This information is provided for informational purposes only. It is not intended to be used as a repair recommendation and we are not responsible for any action you take on any vehicle. All information on this site is protected by copyright.

Add a comment