Fuel Pump: Description and Operation

The fuel tank in All Wheel Drive (AWD) vehicles is divided into two chambers. The electric Fuel Pump (FP) unit (with fuel pump) -1- is in the right chamber. Pump -2- is designed to empty the left chamber -3-.

The Fuel Pump (FP) not only delivers fuel to the engine, it also operates the secondary fuel pump.

For this, it creates an operating stream that is pressed into the secondary fuel pump via a jet which causes acceleration This acceleration causes the fuel in the left chamber of the fuel tank to be drawn into the right chamber of the fuel tank.

In this way, the left chamber of the fuel tank is emptied first, so that there is always enough fuel in the right chamber for the Fuel Pump (FP).

Disturbances caused by a defective secondary fuel pump







If the secondary fuel pump -2- is not functioning, up to 15 liters of fuel -3- (up to about 1/4 of tank capacity) can remain in the left portion of the fuel tank that cannot be drawn out by the Fuel Pump (FP).

If the vehicle will not run due to lack of fuel although the tank is about 1/4 full, proceed as follows:
- Check Fuel Pump (FP). Refer to "Fuel Pump, Electrical Testing (All Wheel Drive)", Testing and Inspection

If the Fuel Pump (FP) is OK, but no fuel is being pumped:
- Add about 5 liters of fuel to the tank.
- Start engine.

If the engine starts now:
- Replace secondary fuel pump. Refer to "Secondary Fuel Pump, Removing and Installing (All wheel drive)", Service and Repair