Fuel Pump Module - Operation

OPERATION





The way the fuel pumps work is as follows, fuel enters the reservoir of the main fuel pump module (driver side). The main fuel pump module (2) pumps the fuel through the filter to the auxiliary fuel pump module (1) (passenger side) through a supply line inside the fuel tank. The fuel pressure regulator inside the auxiliary fuel pump module regulates the pressure at 58 psi and sends fuel to the engine. All unused fuel that is not sent to the engine is fed through a venturi at the bottom of the auxiliary fuel pump module. This creates a low pressure siphoning effect and draws fuel from the passenger side of the tank and transfers it to the drivers side tank via siphon hose inside the tank. While the vehicle is running the fuel in the passenger side of tank is continuously transferred to the drivers side. Fuel will continue to fill the drivers side tank till it reaches the bridge and then starts to spill over to the passenger side.
Both main and auxiliary fuel pumps have fuel level sender cards and the reading of these senders are averaged out to give us the fuel gauge reading. When diagnosing a fuel level sender concern, the passenger side reading should never be higher than the drivers side reading. However it is possible, depending on fuel level and driving habit before diagnosing, to spill fuel over to the passenger side that might indeed show a lower resistance value than the driver side.

The fuel gauge gives an indication to the vehicle operator the level of fuel in the fuel tank. This fuel gauge is controlled by the instrument cluster circuit board based upon cluster programming and a hard wired inputs received by the cluster from the fuel level sending units integrated into the fuel pump modules.

The instrument cluster continually monitors both fuel pump sender cards to determine the level of fuel in the fuel tank. The cluster then sends the proper fuel level messages to other electronic modules in the vehicle over the Controller Area Network (CAN) data bus. For further diagnosis of the fuel gauge or the instrument cluster circuitry that controls the gauge Testing and Inspection. The fuel gauge is serviced as a unit with the instrument cluster.

The technician needs to order the correct part when replacing the main fuel pump module, auxiliary fuel pump module and/or fuel tank as all are replaced individually.