According to the service manual that message means it is not getting a proper signal from the carriage board. Based on the fact you do have power to the carriage board the manual says replace the carriage board itself, if that didn't fix it then engine pca next, then lastly the trailing cable.
Before replacing any parts I would inspect the trailing cable (the one with the larger connection) for any damage and make sure that the connection on both ends are seated well. We just serviced a L360 that had a trailing cable where the shielding was broken in about 6 different spots.