The presupply pump is located in the fuel tank. It is switched on and off by means of a relay and delivers the fuel via the fuel filter to the injection pump.
Although the engine remains operable in the event of the presupply pump failing because the injection pump is equipped with its own vane pump the engine may still stall (die) suddenly during operation.
The relay and relay activation are monitored but not the pump itself. Fault code 73 "fuel presupply pump" is stored in the case of defect.