Fuel Pump, Checking

Fuel Pump, Checking

=> [ Fuel Pressure, Checking ]

=> [ Fuel Delivery, Checking ]

Special tools, testers and auxiliary items required

• Pressure Tester (Diesel) (VAS 6551)

• Hose (VAS 6551/2)

• Connection Fitting (VAS 6551/5-1)

• Hose (VAS 6551/5-2)

• Hose (VAS 6551/5-3)

• Hose (VAS 6551/5-4)

• Vehicle Diagnostic Tester

• Measuring Container

• Wiring Diagram

Fuel Pressure, Checking

- Read the safety precautions before starting. Refer to => [ Safety Precautions ] Safety Precautions.

- Follow the guidelines for cleanliness. Refer to => [ Clean Working Conditions ] Clean Working Conditions.

Test Conditions

• The Engine Control Module (ECM) Diagnostic Trouble Code (DTC) memory does not contain a malfunction related to the voltage supply of the fuel pump.

• The fuel pump control module is OK.

• The battery charger is connected.

• The fuel pump fuse is OK.

• The fuel filter is OK.

• Fuel tank is at least 3/4 filled.

• The ignition is off

The fuel supply line is under pressure. Wear protective goggles and protective clothing in order to avoid injury and contact with the skin. Wrap a cloth around the connection before removing a fuel hose. Then release pressure by carefully loosening the union nut.

- Disconnect the fuel supply line - 1 - from the fuel filter.






- Connect the pressure tester (diesel) (VAS 6551) with the hose (VAS 6551/2) , the hose (VAS 6551/5-2) and the connection fitting (VAS 6551/5-1) as illustrated.






• Make sure the hose clamps are tight.

• Secure the hoses with the included clamps.

- Open the shut off levers "A" and "B" on the pressure tester (diesel) (VAS 6551) in the direction of flow.






- Close the shut off lever "C".

- Press the ON/OFF button to turn on the pressure tester (diesel) (VAS 6551).

- Turn on the ignition.

- Connect the vehicle diagnostic tester and conduct the guided function "activate fuel pump".

- Select "check fuel pressure".

• The fuel pump is now activated.

- Read off the pressure on the pressure tester (diesel) (VAS 6551). Specified value: approximately 4.0 bar.

- Slowly close the shut off lever "B" on the pressure tester (diesel) (VAS 6551).

- Read the pressure on the pressure tester (diesel) (VAS 6551) , whose specified value should be > 6.0 bar.

- Turn off the ignition.

If the specification value is achieved

- Check the fuel delivery. Refer to => [ Fuel Delivery, Checking ].

If the specification is not obtained

• If the pressure tester (diesel) (VAS 6551) is to be removed, open the shut off lever "C" and reduce the residual pressure. For this purpose, hold the hose from the shut off lever "C" in a measuring container.

- Remove the pressure tester (diesel) (VAS 6551) and connect the fuel supply line to the fuel filter.

- Make sure the hose clamps are tight.

- Remove the right rear seat or seat back.

- Fold the right carpet cutout to the side.






- Remove the flange cover nuts - 1 through 4 - and flange cover.

- Disconnect the fuel supply line - 2 -. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.






- Connect the pressure tester (diesel) (VAS 6551) to the hose (VAS 6551/5-3) and the hose (VAS 6551/5-4) as shown.






- Open the shut off levers "A" and "B" on the pressure tester (diesel) (VAS 6551) in the direction of flow.






- Close the shut off lever "C".

- Turn on the ignition.

- Perform the guided function "activate fuel pump" again.

- Select "check fuel pressure".

• The fuel pump is now activated.

- Read off the pressure on the pressure tester (diesel) (VAS 6551). Specified value: approximately 4.0 bar.

- Slowly close the shut off lever "B" on the pressure tester (diesel) (VAS 6551).

- Read the pressure on the pressure tester (diesel) (VAS 6551) , whose specified value should be > 6.0 bar.

- Turn off the ignition.

If the target values are achieved

- Check the fuel supply line from the fuel tank to the fuel filter for damage.

If the specifications are not obtained again

- Make sure all couplings and fuel lines in the fuel tank and the fuel delivery unit are secure and not leaking.

If no malfunction can be found:

- The fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit and Fuel Level Sensor ] Fuel Delivery Unit and Fuel Level Sensor.

• If the pressure tester (diesel) (VAS 6551) is to be removed, open the shut off lever "C" and reduce the residual pressure. For this purpose, hold the hose from the shut off lever "C" in a measuring container.

Fuel Delivery, Checking

Test Conditions

• The Engine Control Module (ECM) Diagnostic Trouble Code (DTC) memory does not contain a malfunction related to the voltage supply of the fuel pump.

• The fuel pump control module is OK.

• The battery charger is connected.

• The fuel pump fuse is OK.

• The fuel filter is OK.

• Fuel tank is at least 3/4 filled.

• The ignition is off.

• A second mechanic is needed for the following procedure.

- Read the safety precautions before starting. Refer to => [ Safety Precautions ] Safety Precautions.

- Follow the guidelines for cleanliness. Refer to => [ Clean Working Conditions ] Clean Working Conditions.

- Connect the pressure gauge (diesel) (VAS 6551) with the hose (VAS 6551/2) , the hose (VAS 6551/5-2) and the connection fitting (VAS 6551/5-1) as illustrated.






• Ensure proper seating of the hose clamps.

• Secure the hose lines with the included clamps.

- Hold the open end of the hose (VAS 6551/5-2) in a measuring container.

- Open the shut off levers "A" and "B" on the pressure tester (diesel) (VAS 6551) in the direction for flow.






- Close the shut off lever "C".

- Press the ON/OFF button to turn on the pressure gauge (diesel) (VAS 6551).

- Perform the guided function "activate fuel pump".

- Select "check delivery quantity".

• The fuel pump now runs for 30 seconds.

- Slowly close the shut off lever - B - until a counterpressure of 4 bar is achieved.

- Empty the measuring container.

- Perform the guided function "activate fuel pump" again.

- Select "check delivery quantity".

• The fuel pump now runs for 30 seconds.

Minimum delivery rate specified value: > 1.7L/30 seconds.

If the specification is not obtained

• If the pressure tester (diesel) (VAS 6551) is to be removed, open the shut off lever "C" and reduce the residual pressure. For this purpose, hold the hose from the shut off lever "C" in a measuring container.

- Remove the pressure tester (diesel) (VAS 6551) and connect the fuel supply line to the fuel filter.

- Make sure the hose clamps are tight.

- Remove the right rear seat or seat back.

- Fold the right carpet cutout to the side.






- Remove the flange cover nuts - 1 through 4 - and flange cover.

- Disconnect the fuel supply line - 2 -. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.






- Connect the pressure tester (diesel) (VAS 6551) to the hose (VAS 6551/5-3) and the hose (VAS 6551/5-4) as shown.






- Hold the open end of the hose (VAS 6551/5-3) in a measuring container - 1 -.

- Open the shut off levers "A" and "B" on the pressure tester (diesel) (VAS 6551) in the direction of flow.






- Close the shut off lever "C".

- Turn on the ignition.

- Perform the guided function "activate fuel pump".

- Select "check delivery quantity".

• The fuel pump now runs for 30 seconds.

- Slowly close the shut off lever - B - until a counterpressure of 4 bar is achieved.

- Empty the measuring container.

- Perform the guided function "activate fuel pump" again.

- Select "check delivery quantity".

• The fuel pump now runs for 30 seconds.

Minimum delivery rate specified value: > 1.7L/30 seconds.

If the specification is now obtained

- Check the fuel supply line to the fuel filter for kinks and damage.

If the specification is again not obtained

- Replace the fuel delivery unit.

• If the pressure tester (diesel) (VAS 6551) is to be removed, open the shut off lever "C" and reduce the residual pressure. For this purpose, hold the hose from the shut off lever "C" in a measuring container.