Powertrain, generic · Computer and auxiliary outputs

P0620 Generator Control Circuit

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

The alternator regulator is linked to the engine module by an L (turn-on) line, an F (field) line reporting field load as a duty cycle, or on newer cars a LIN bus. P0620 is the general control circuit code. On LIN alternators it stands for disturbed control or communication: a manufacturer table published via NHTSA (gateway module with LIN alternator) lists it with the battery lamp on and stop-start disabled, alongside P065B for range/performance. Saab's 9-3 diesel uses it for the L line – open between module and alternator for more than 6 s, or a charging signal in an implausible state. Ford's 6.8 L V10 reports it with or without the check engine light depending on the variant. GM does not use P0620 and reports L and F line faults as P0621/P0622.

Likely causes

Connector or wire between module and alternator (corrosion, break, chafing)
Alternator or regulator faulty, including its LIN interface
Battery flat or faulty, jump start or charger connected
Loose or worn drive belt
Engine module or gateway (software, driver)

Symptoms

  • Battery warning lamp on
  • Battery not or incorrectly charged, starting problems
  • Stop-start not working
  • Sometimes no noticeable symptoms

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–700
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

alternatorvoltage regulatorgenerator wiringengine control module

Related codes

P0621P0622P065BP0562P0563P2500

References: law.cornell.edu, static.nhtsa.gov, saabwisonline.com, saabwisonline.com.