P0620
Generator Control Circuit
Charging / computer output
Generic OBD-II
High
What it means
P0620 means the ECM has detected a problem in the circuit it uses to command and monitor the alternator (generator). If the alternator can't charge correctly, the battery gradually discharges, which can bring on warning lights, electrical glitches, and eventually a no-start. Because it affects the charging system, it's worth diagnosing promptly.
High
Can I keep driving? Risky — if the alternator isn't charging properly the battery can run down and leave you stranded, so treat a charging fault as urgent.
Common symptoms
What you'll notice
- Check-engine light on, often with the battery/charging warning light
- Battery runs down or the car is hard to start
- Dimming or flickering lights and other electrical glitches
- Possible no-start if the battery fully discharges
Common causes
Most likely first
- Failed alternator (generator) or its internal voltage regulatorLikely
- Open, shorted, or corroded generator control-circuit wiringCommon
- Poor ground or loose charging connectionCommon
- Failed engine control module (rare)Less often
How to diagnose & fix
Work through it in order
- Measure charging voltage at the battery with the engine running — it should sit around 13.5–14.5V.
- Inspect the generator control-circuit wiring and connectors for opens, shorts, and corrosion.
- Check battery and alternator grounds and the main charging connections.
- Bench-test or replace the alternator/regulator if the control circuit is intact. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P0620?+
Not for long. If charging is impaired the battery will slowly drain, dashboard warnings may appear, and the car can eventually stall or fail to restart.
Can I just clear P0620?+
Clearing it won't restore charging — if the alternator or its control circuit is faulty the battery keeps draining and the code returns.
Related codes
Often seen with P0620
Read & clear P0620 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX