P0620 OBD-II Trouble Code: Generator Control Circuit Malfunction

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Cost of diagnosing the P0620 code

P0620 is a diagnostic trouble code (DTC) for "Generator Control Circuit Malfunction". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic for $70.00. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $30.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

Cars Estimate Credit towards follow-up repair Earliest Availability
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Toyota$70.00$30.00
BMW$70.00$30.00
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P0620 code definition

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

What the P0620 code means

The PCM controls your vehicle’s generator through a generator turn-on signal circuit, allowing it to turn the generator off and on. When the generator needs to come on, the PCM sends a five-volt signal through the generator turn-on signal circuit to the voltage regulator. Doing so allows the voltage regulator to start controlling the generator field circuit.

As soon as the generator is enabled, the voltage regulator can control the generator output independent of the PCM. Under some operating conditions, the PCM can turn off the five-volt signal and, thus, turn off the generator too.

The PCM also has fault-detection circuitry to monitor these operations. If it detects an unexpected voltage or any other problem, it can cut or reduce the power. This is also when the P0620 code gets stored.

What causes the P0620 code?

There are a number of reasons your vehicle’s PCM may record a P0620 code. These would be:

  • The voltage regulator has malfunctioned
  • The generator is faulty
  • A battery charge
  • The generator circuit is suffering from a poor electrical connection
  • The generator harness is open or shorted
  • The PCM is faulty (this one is the least likely cause)

What are the symptoms of the P0620 code?

When the P0620 code is stored, you should see your Check Engine Light come on. Unfortunately, that’s about the only noticeable symptom associated with this code.

How does a mechanic diagnose the P0620 code?

Your mechanic will use an OBD-II scanner to check which trouble codes your vehicle has stored. They’ll then check the generator for any signs of a bad connection or damage that may have caused a misread of the voltage. The various circuits associated with the generator will have to be looked at too. All the wires involved with this component will also need to be examined, as well as the connectors.

If everything else checks out, the mechanic will check the PCM to make sure it didn’t store the code erroneously.

Common mistakes when diagnosing the P0620 code

This problem can be a difficult one to properly diagnose, which is why it’s important your mechanic doesn’t immediately just assume the PCM was in error. To make sure it’s not the fault of the PCM, the system should be cleared and a test drive conducted to see if the code returns.

Otherwise, the mechanic could replace your PCM needlessly – and charge you in the process – when something like the wiring was actually responsible.

How serious is the P0620 code?

Although it may seem like a minor problem because there aren’t any noticeable symptoms, the P0620 code is still something you’ll want to get repaired ASAP. The transfer of electricity and your vehicle’s generator are both important to its overall functioning and code P0620 could be the beginning of a much bigger problem if you don’t address it right away.

What repairs can fix the P0620 code?

Your mechanic will probably have to do one of the following:

Again, this last option is almost never necessary.

Additional comments for consideration regarding the P0620 code

The same problem that caused the P0620 code to be stored could also be behind others. Just because there isn’t a problem code stored for those yet doesn’t mean your mechanic shouldn’t take the time to do a thorough inspection and ensure other parts of your vehicle aren’t suffering because of abnormal voltages.

Need help with a P0620 code?

YourMechanic is here to make it as convenient as possible to have your vehicle diagnosed and repaired. Just complete this online form for a quick quote and to schedule your appointment. You can even give us a call at 1-800-701-6230 to speak with a friendly service advisor. Once your appointment comes, a certified mobile mechanic will come to your home or office to handle repairs on the spot.

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