A coupling system includes an optical plug-in connector, a coupling partner and a retaining element. The method comprises: recording a first fuel injection quantity; commanding a fuel rail pressure high; recording a second fuel injection quantity while the fuel rail pressure is high; and diagnosing the fuel injector as contaminated if the first fuel injection quantity is greater than the second fuel injection quantity. The first and second electrode down-leads are parallel to each other. The write ordering style service utilizes the loosely-accurate global clock to provide consistent replication of a storage space of the consistency group.