Skip to content
P0621 Powertrain

Generator Lamp L Control Circuit

The control circuit for the generator warning lamp output (L terminal) reports a fault.

Affected components

  • Alternator
  • Alternator wiring

Common causes

  • High likelihood: Lamp circuit open or shorted
  • Medium likelihood: Alternator regulator fault

Possible symptoms

  • Check engine light on
  • Possible limp mode or no-start
  • Multiple follow-up faults across modules
  • Reset/relearn may be needed after repair

Diagnostic notes

  • The malfunction indicator lamp may illuminate

Related codes

Sources

Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.

You might like