Technical Description of OBD-II Trouble Code
Malfunction in the Generator Control Circuit
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Hyundai, Mercedes-Benz, Buick, Ford, GMC, Chevrolet, Jeep, Cadillac, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P0620 indicates that the powertrain control module (PCM) has detected a malfunction in the generator control circuit.
Typically, the PCM activates and monitors the generator control circuit whenever the engine is running.
Every time the ignition is turned on and the PCM is activated, multiple self-tests are performed by the controller. In addition to running internal self-tests, the controller area network (CAN) is used to compare signals from each individual module to ensure proper interaction between the various controllers.
If a problem is detected in monitoring the generator control circuit, a code P0620 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 for MIL illumination.
A typical alternator:
What is the severity of this DTC?
Internal control module codes should always be taken seriously. A stored code P0620 could result in various drivability concerns, including a no-start condition and/or a dead battery.
What are some of the symptoms of the code?
Symptoms of a P0620 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0620 troubleshooting steps?
To diagnose a code P0620, you will need a diagnostic scanner, a battery/alternator tester, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information.
Refer to your vehicle information source for any technical service bulletins (TSB) that are related to the stored code, vehicle (year, make, model, and engine), and exhibited symptoms. If you find a relevant TSB, it may provide diagnostic information that can greatly assist you.
Start by connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and freeze frame data. It is important to write down this information in case the code is intermittent. After recording all relevant information, clear the codes and test drive the vehicle until the code is reset or the PCM enters readiness mode. If the PCM enters readiness mode, the code is intermittent and will be more challenging to diagnose. In some cases, the condition that caused the P0620 to be stored may need to worsen before a diagnosis can be made. If the code is reset, continue with your diagnosis.
Use the battery/alternator tester to check the battery and ensure that it is adequately charged. If it is not, test the alternator/generator. Follow the manufacturer’s recommended specifications for minimum and maximum voltage output requirements for the battery and alternator. If the alternator/generator is not charging, proceed to the next step in your diagnosis.
Refer to your source of vehicle information to obtain connector face views, connector pin-out charts, component locators, wiring diagrams, and diagnostic flow charts that are relevant to the code and vehicle in question.
Check if there is battery voltage at the alternator/generator by using the appropriate wiring diagram and your DVOM. If there is no voltage, check the system fuses and relays and replace any defective parts as necessary. If all fuses and relays are functioning properly, suspect that the alternator/generator is faulty.
If the alternator is charging and the P0620 continues to reset, use the DVOM to test the power supply fuses and relays for the controller. Replace any blown fuses as necessary. Fuses should be tested with the circuit loaded.
If all fuses and relays appear to be functioning as intended, visually inspect the wiring and harnesses related to the controller. Also, check the chassis and engine ground junctions. Use your vehicle information source to obtain ground locations for the relevant circuits. Use the DVOM to test the integrity of the grounds.
Visually inspect the system controllers for any signs of water, heat, or collision damage. Any damaged controller, especially due to water, should be considered defective.
If the controller power and ground circuits are intact, suspect a defective controller or a controller programming error. Controller replacement will require reprogramming. In some cases, reprogrammed controllers may be available through aftermarket sources. Other vehicles/controllers may require on-board reprogramming that can only be done through a dealership or another qualified source.
