P0620 to P0626: alternator control circuits
The engine computer has found a fault in the alternator's control circuit, its warning lamp circuit or its field (F terminal) circuit.
SeverityHighCarrying on can cause expensive damage, so deal with it now.
Can you keep driving?Only as far as the workshopWhat does P0620 mean?
On many modern cars the engine computer controls how hard the alternator charges, through a control or field circuit, and reads its state back. These codes mean that conversation has broken down. The alternator may then stop charging altogether, or charge at a fixed rate. If it stops, the car runs on the battery alone until it is flat.
What causes P0620?
- A broken wire or corroded connector at the alternator
- A failed voltage regulator inside the alternator
- A worn alternator
- A blown fuse or a poor ground in the charging circuit
What to check first for P0620
- Measure the voltage at the battery with the engine running: it should be clearly above the engine-off reading
- Inspect the alternator's connector and the main charging cable
- Check the auxiliary belt is driving the alternator
- Have the alternator and its regulator tested
Can you drive with P0620?
Drive only to a workshop or home, with as little electrical load as possible. If the battery warning light is on, the car may stop when the battery runs flat, which on a busy road is dangerous.
Since May 2018 an engine warning light that stays on is a major defect at the MOT, so the car fails until the fault is fixed.
Codes on this page
- P0620Generator Control Circuit
- P0621Generator Lamp/L Terminal Circuit
- P0622Generator Field/F Terminal Circuit
- P0623Generator Lamp Control Circuit
- P0625Generator Field/F Terminal Circuit Low
- P0626Generator Field/F Terminal Circuit High
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
