P0620: Generator control: circuit fault
The ECU detects a problem in the circuit it uses to control alternator charging. Usually the wiring, the plug or the alternator itself.
| Code | P0620 |
|---|---|
| System | Engine and transmission |
| Group | P06xx, Control unit and auxiliary outputs |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0620 means
On many cars the engine ECU decides how much the alternator should charge, depending on demand and battery condition. This code means the control circuit between the ECU and the alternator is not working properly. If the alternator stops charging, the car will eventually run the battery flat.
Most common causes
- Alternator plug loose, dirty or corroded
- Control wire between ECU and alternator broken or chafed
- Faulty alternator regulator
- Faulty alternator
- Poor alternator earth
Symptoms
- Engine warning light and often the battery light on
- Battery going flat
- Lights changing brightness
Can you drive with P0620?
With care If the alternator is not charging, the car will only run until the battery is exhausted. Keep driving to a minimum and get it checked soon.
How to check it
With the engine running, check the control module voltage on the scan tool: it should sit around 13.5 to 14.5 volts. If it stays near 12 or keeps dropping, the alternator is not charging.
How to read and clear P0620 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0620 with this same explanation and whether it’s confirmed, pending or permanent.
With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.
Similar codes
- P0607 Control module performance
- P0615 Starter relay: circuit fault
- P0616 Starter relay: circuit low
- P0617 Starter relay: circuit high
- P0621 Generator lamp L control: circuit fault
- P0622 Generator field F control: circuit fault
- P0627 Fuel pump A control: circuit open or faulty
- P0638 Throttle actuator control: range or performance (bank 1)
- P0600 Serial communication link fault
- P0601 Internal control module memory checksum error
- P0602 Control module programming error
- P0603 Internal control module keep alive memory (KAM) error
P0620 is a generic code, so it means the same on any make, for example on Audi, Fiat, Mazda, Opel / Vauxhall, Peugeot, Toyota. See what Final OBD does on your car in makes and models.
What does code P0620 mean?
On many cars the engine ECU decides how much the alternator should charge, depending on demand and battery condition. This code means the control circuit between the ECU and the alternator is not working properly. If the alternator stops charging, the car will eventually run the battery flat.
Can you drive with P0620?
If the alternator is not charging, the car will only run until the battery is exhausted. Keep driving to a minimum and get it checked soon.
How do you clear P0620?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0620 comes back.
Read it on your car
Final OBD reads the faults of every control unit for free, including each make’s own codes, and with Pro explains each one in plain English. Free clears engine faults at no cost.
Coming soon
Mid to late October 2026
If you want to try it in your car before anyone else, send us your email and we will add you as a tester.
info@finalobd.com