KlaroFault codeP0621
MODERATEGenerator Lamp L Control Circuit Malfunction
What this code means
Generator Lamp L Control Circuit Malfunction.
P0621 is a generic code: it means the same thing on every make. P0621 belongs to family P06xx — Control unit and output circuits. Its page explains how to read a code and groups all its codes by part.
Type of fault
The control unit has detected an electrical anomaly on this circuit without saying exactly which. Diagnosis starts with a visual check of the wiring and connector, then measuring the component — resistance, supply, ground — with a multimeter.
Alternator (charging system)
The alternator recharges the battery and powers the car while the engine runs. On modern cars the control unit drives its output voltage, and it monitors the charging warning light and the regulator.
What you notice
Battery warning on the dashboard, a battery that goes flat, dimming lights; on some cars the control unit switches off comfort functions.
How to check it
With the engine running, the control module voltage in Klaro should be around 13.5 to 14.7 V. Check the alternator's belt, its connectors and the thick charging cable. A voltage that stays at battery level means the alternator is not charging.
Watch it live in Klaro
With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:
- Control module voltage
What to do
Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.
Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →
How to read this code
- PPowertrain
- 0standardised code
- 6Control unit and output circuits
- 21P0621
