Circuit/System Description
An electric fuel pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel pump is part of the diesel fuel conditioning module (DFCM) assembly. The fuel pump is powered by the fuel pump relay. The fuel pump relay is controlled by the engine control module (ECM). The ECM enables the fuel pump when the ignition is turned on and will continue to run for two minutes or until the engine starts. If the engine does not start due to low fuel pressure and the ignition is left in the ON position; the pump will run for up to two minutes or until the ignition is turned off. The ECM will also turn off the fuel pump if incorrect voltage is detected on the control circuit. The ECM will need to be powered down with a key cycle during diagnosis or after repairs, before it will command the fuel pump on again.