P0621: Generator lamp L control: circuit fault
The ECU detects a fault in the alternator L circuit, the one linked to the charge warning light. Usually wiring, the plug or the alternator.
| Code | P0621 |
|---|---|
| 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 P0621 means
The alternator’s L terminal is linked to the battery warning light on the dashboard and to exciting the alternator at start-up. This code means that circuit is not working as it should. Exactly how this terminal is used varies from one manufacturer to another.
Most common causes
- Alternator plug loose or corroded
- L terminal wire broken or chafed
- Blown fuse in the charging circuit
- Faulty alternator regulator
- Faulty alternator
Symptoms
- Engine warning light on
- Battery warning light on, or never lighting up
- Battery not charging properly
Can you drive with P0621?
With care The alternator may not be charging and the battery could go flat. Drive with care and get it checked soon.
Open the bonnetthe in-depth explanation
How to check it
With the ignition on and the engine off, the battery warning light should come on and then go out once the engine starts. Also check the running voltage on the scan tool: if it does not go above about 13 volts, it is not charging.
How to read and clear P0621 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 P0621 with its description and whether it’s confirmed, pending or permanent.
If the engine stores it over standard OBD, with FREE you read this code with its explanation for nothing and clear it. With PRO you also read the faults of every control unit and clear them in all of them.
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 an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P061D The internal control unit motor air mass gives readings outside the normal range
- P061E The internal control unit brake signal gives readings outside the normal range
- P061F The internal control unit throttle actuator controller gives readings outside
- P0620 Generator control: circuit fault
- P0622 Generator field F control: circuit fault
- P0623 The generator light control has an electrical fault
- P0624 The circuit controlling the fuel filler cap warning lamp has a fault
- P0625 The generator field terminal gives a lower signal than normal
- 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
What does code P0621 mean?
The alternator’s L terminal is linked to the battery warning light on the dashboard and to exciting the alternator at start-up. This code means that circuit is not working as it should. Exactly how this terminal is used varies from one manufacturer to another.
Can you drive with P0621?
The alternator may not be charging and the battery could go flat. Drive with care and get it checked soon.
How do you clear P0621?
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, P0621 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
