What are the common causes of P0620?

A failed alternator. A failed voltage regulator. A wiring fault in the generator control circuit. A bad battery or battery sensor. A faulty PCM control output.

Check the drive belt and battery condition. Inspect the generator control circuit wiring and connectors. Measure charging voltage at the battery. Test the voltage regulator and replace if faulty. Replace the alternator if control is fine but output is low. Clear the code and retest.

P0620

Generator Control Circuit

System: Computer output circuits (P code)
Lamp: Check Engine Light
Category: Powertrain - Computer and Auxiliary Controls

What it means

P0620 means Generator Control Circuit.

Check these first

A failed alternator
A failed voltage regulator
A wiring fault in the generator control circuit
A bad battery or battery sensor
A faulty PCM control output

What to do next

Check the drive belt and battery condition
Inspect the generator control circuit wiring and connectors
Measure charging voltage at the battery
Test the voltage regulator and replace if faulty
Replace the alternator if control is fine but output is low
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.