The DDE 4.1 features an electric fuel supply pump located in the fuel tank. The DDE master control unit switches the pump on and off via a relay. This pump delivers fuel via the fuel filter to the high pressure pump. The high pressure pump itself additionally features a mechanically driven gear pump that draws in the fuel via the fuel filter.
The engine remains operable in the event of the in-tank pump failing, however, it may cut out under high loads or when the fuel level is low.
The relay and relay activation are monitored but not the pump itself. Fault code 1250 "Relay presupply pump" is stored in the event of a defect in the relay.