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.

Real-world scan data

Seen in

707

scans in the past year

Found in

0.1%

of scans

0.2%

of scans that found faults

Appears alongside · share of P0620 scans

P0300in 11.0% of scans

P0626in 9.9% of scans

P0113in 7.5% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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.

Read & clear P0620 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX