DTC P0621: Generator "L" Terminal Circuit: Description

Terminal "L" circuit (Red wire) is link between ECM and generator. ECM supplies generator with 12 volts whenever ignition is on. Once engine is running, generator must have 12 volt supply to charge. If engine is not running, or generator stops charging while engine is running, it will ground this 12 volt supply from ECM. When ECM detects this low voltage state, it will send a message to BCM over CAN link, which will send a message to instrument cluster over Class II link to illuminate charge light. DTC sets when voltage at generator terminal "L" input is high when engine is not running.