Fuel Pump: Description and Operation

CONTROL OF THE FUEL PUMP

The ECM activates the main relay (2/32) when the ignition is switched ON. The fuel pump relay (2/23) is activated simultaneously for one second to enable the pump (6/31) to develop pressure.

As the engine is turned by the starter motor, the RPM sensor (7/25) and CMP sensor (7/21) deliver engine speed and crankshaft position signals to the ECM, which activates the fuel pump relay.

B5234T/B5234T5: The fuel pump functions continuously when the engine operates.

B52S4S: There is a two-stage function for the fuel pump to reduce the pressure in the fuel tank. This in turn means a lower pressure for the EVAP system. The fuel pump works at full power at start-up and up to 500 rpm, at reduced effect between 500 and 3000 rpm and then once again at full power at engine speeds above 3000 rpm. The fuel pump's power is controlled via the fuel pump relay and a ballast resistor (20/11).