Due to the nature of operations on the Johnsonville Branch and the need to increase the nominal catenary voltage for full Matangi operation, operation of the Johnsonville Branch needed to be cut over immediately rather than phased in as elsewhere on the network. This caused issues due to delays in the introduction of further Matangi units and the voltage increase which led to a number of electrical failures on the older DM/D sets. As the sets deteriorated in condition they were withdrawn from service, allowing cars with little or no problems to be combined in place of failed cars in order to maintain service.