P0621 - GENERATOR LAMP L CONTROL CIRCUIT MALFUNCTION

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.

• Check Engine light ON.
• Motor starting problems.
• The engine stops at idle.
• Difficulty in making gear changes.

DTC P0621 OBD2 is set by the following reasons:

• The generator lamp control circuit L may be open or shorted.
• The alternator/generator may be damaged.
• The generator lamp may be faulty.

To troubleshoot the P0621 OBDII fault code, try this:

• Consult the Technical Service Bulletins (TSB).
• Verify that the wires and connectors of circuit L of the generator lamp are not damaged because of high temperatures or water. If you observe that one of these components presents these deficiencies, make the appropriate corrections.
• Check that the battery is charged and is receiving the amount of voltage from the alternator as specified by the manufacturer. If you determine that it is not receiving the required voltage, follow the recommended instructions in the service manuals to solve the problem.
• If after performing the above checks you realize the alternator and lamp are working properly, check the fuses and relay circuit. If one of these is damaged, make the necessary repairs.