The high pressure fuel pump is the interface between the low pressure and the high pressure stages. Under all operating conditions, it is responsible for providing adequate high pressure fuel through out the vehicle's complete service life. This also includes the provision of extra as needed for rapid starting and for rapid build-up of pressure in the rail. The high pressure pump continually generates the system pressure as needed in the high-pressure accumulator (common rail). This means therefore, that in contrast to conventional systems, the fuel does not have to be specially compressed for each individual injection process.

A: Fuel inlet (From fuel tank via fuel filter)

B: Fuel outlet (To common rail)

C: Fuel return (To fuel tank)

D: Fuel return (From injector)