The generator lamp warns the driver of load problems. This lamp is located on the instrument panel, and it is continuously monitored by the Powertrain Control Module (PCM). The PCM will perform continuity measurements of the L-control circuit once the car’s engine starts. In addition to these measurements, the Control Area Network (CAN) compares the signals from each module to ensure they are correctly synchronized with each other.
The diagnostic code P0621 OBDII will be stored when the PCM detects a malfunction in the generator lamp L control circuit.