Transfer Fuel Pump (G6), Checking

Transfer Fuel Pump (G6), Checking

=> [ Delivery Rate and Fuel Delivery Quantity, Checking ]

=> [ Voltage Supply, Checking ]

=> [ Current Draw, Checking ]

First, make sure the connector is secure on the fuel delivery unit by pulling on it without opening the locking mechanism.

- Remove the rear seat bench.

- Remove the flange cover - 1 - using the trim removal wedge (3409) - arrows -.

- Pull on the connector - 1 - without pressing the release to make sure the connection is secure. If the connector was not connected correctly, it could cause a fault.

Delivery Rate and Fuel Delivery Quantity, Checking

Special tools, testers and auxiliary items required

• Vehicle tester

• Connection Fitting (VAS 6551/5-1)

• Hose (VAS 6551/2)

• Hose (VAS 6551/1)

• Pressure Tester (Diesel) (VAS 6551)

• Hose connections are secured with either spring-type or clamp-type clips.

• Replace the locking clamps with spring clamps.

• Hose clip pliers (VAS 6362) are recommended for installing spring-type clamps.

Test Conditions

• The fuses must be OK.

• Connect the battery charger to make sure the voltage supply is a minimum of 12.5 volts.

• Minimum fuel level in the fuel tank: 15 liters

• Make sure the vehicle is level.

• The fuel hoses and lines inside the engine compartment and on the underbody are not pinched due to damage (bent).

• All electrical consumers such as, for example, lights and rear window heater, must be turned off.

• The vehicle must be fueled with diesel fuel treated for the season. Diesel fuel sold in the summer must be able to be filtered down to 0 °C (32 °F) and during the transition time down to -10 °C (14 °F), and in the winter down to -20 °C (-4 °F). Under some conditions, summer diesel fuel can coagulate at low winter temperatures. If not sure, take a sample of the winter fuel and let it stand at low outside temperatures for approximately 1 hour. If the fuel coagulates at temperatures down to -20° C (-4 °F), then this diesel fuel is not suited for low temperatures. This coagulation can plug the screen in the fuel delivery unit as well as in the fuel filter.

The fuel supply line remains 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. Remove the hose connection carefully to release the pressure.

High Pressure Pump Test Sequence

- Remove the engine cover.

- Open the clamp and remove the fuel supply line - arrow - from the high pressure pump.

- Attach the connecting fitting (VAS 6551/5-1) into the supply line and secure it with a clamp.

- Connect the hose (VAS 6551/2) between the connection fitting (VAS 6551/5-1) and connection "A" on the pressure tester (diesel) (VAS 6551).

- Connect the hose (VAS 6551/1) to the connection B on the pressure tester (diesel) (VAS 6551).

- Place the open end of the hose (VAS 6551/1) into a suitable measuring container.

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

- Open the shut off levers "A and B" on the pressure tester (diesel) (VAS 6551) and close the shut off lever "C".

- Connect the hose (VAS 6551/2) between the supply line coming from the fuel tank and connection "A" on the pressure tester (diesel) (VAS 6551).

- Connect the hose (VAS 6551/1) to connection "B" on the pressure tester (diesel) (VAS 6551).

- Place the open end of the hose (VAS 6551/1) into a suitable measuring container.

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

- Open the shut off levers "A and B" on the pressure tester (diesel) (VAS 6551) and close the shut off lever "C".

- Connect the vehicle diagnostic tester and perform the Guided Function "check electric fuel pump(s)".

• The fuel pump now runs for 30 seconds.

- Close the shut off lever "B" carefully, to set the pressure to 4.5 +/- 0.1 bar.

• If the pressure to be set is not reached, perform the "fuel delivery unit flange test". One reason may be the fuel lines are bent or kinked.

- After adjusting the pressure successfully, empty the measuring container and perform the Guided Function "Checking Electric Fuel Pump(s)" one more time.

- Read the pressure on the pressure tester (diesel) (VAS 6551).

- See how much fuel is in the measuring container after operating the pump (30 seconds). Specified value: minimum. 1100 ml

If the specified values are achieved: The transfer fuel pump is OK, replace fuel filter. Refer to Maintenance Procedures.

If the specified values are not obtained: Perform the "fuel delivery unit flange test".

Fuel Delivery Unit Flange Test

- Disconnect the fuel supply line (black or with a black mark) - 3 - from the fuel delivery unit. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.

- Wipe up any leaking fuel with a cloth.

- Connect the hose (VAS 6551/2) between the supply line on the flange and connection "A" on the pressure tester (diesel) (VAS 6551).

- Connect the hose (VAS 6551/1) to connection "B" on the pressure tester (diesel) (VAS 6551).

- Place the open end of the hose (VAS 6551/1) into a suitable measuring container.

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

- Open the shut off levers "A and B" on the pressure tester (diesel) (VAS 6551) and close the shut off lever "C".

- Connect the vehicle diagnostic tester and perform the Guided Function "check electric fuel pump(s)".

• The fuel pump now runs for 30 seconds.

- Close the shut off lever "B" carefully, to set the pressure to 4.5 +/- 0.1 bar.

• If the pressure to be set is not reached, check the fuel pump current draw. Refer to => [ Current Draw, Checking ].

- After adjusting the pressure successfully, empty the measuring container and perform the Guided Function "Checking Electric Fuel Pump(s)" one more time.

- Read the pressure on the pressure tester (diesel) (VAS 6551).

- See how much fuel is in the measuring container after operating the pump (30 seconds). Specified value: minimum 1100 ml.

If the specified values are achieved: The transfer fuel pump is OK, make sure the fuel lines to the engine are not bent or kinked; replace if necessary.

If the specified values are not obtained: Check the voltage supply to the fuel pump. Refer to => [ Voltage Supply, Checking ].

Voltage Supply, Checking

Special tools, testers and auxiliary items required

• Vehicle tester

• Current Pick-Up (V.A.G 1526 B/2)

• Multi-Meter (V.A.G 1526 D)

• Test Instrument Adapter/DSO (5-pin) (VAS 5565)

Test Conditions

• The fuses must be OK.

• Battery voltage must be a minimum 12 volts. Connect a battery charger if necessary.

• All electrical consumers such as, for example, lights and rear window defogger, must be turned off.

• Wire visual inspection is OK

Test Sequence

- Remove the rear seat bench.

- Remove the flange cover - 1 - using the trim removal wedge (3409) - arrows -.

- Pull on the connector - 1 - without pressing the release to make sure the connection is secure. If the connector was not connected correctly, it could cause a fault.

- Disconnect the connector from the fuel delivery unit flange.

- Install the test instrument adapter/DSO (5-pin) (VAS 5565) between the connectors on the fuel delivery unit and cover.

- Connect the multi-meter (V.A.G 1526 D) to the wires - 1 and 5 - on the test instrument adapter/DSO (5-pin) (VAS 5565).

- Connect the vehicle diagnostic tester and perform the Guided Function "check electric fuel pump(s)".

• The fuel pump now runs for 30 seconds.

- Read the voltage value on the multi-meter (V.A.G 1526 D) : Target value = approximately battery voltage.

If there is no voltage:

- Check the activation of the fuel pump relay and check the wires for an open and/or short circuit. Refer to the vehicle diagnostic tester

If the voltage supply is OK.

- Check the fuel pump current draw. Refer to => [ Current Draw, Checking ].

Current Draw, Checking

Special tools, testers and auxiliary items required

• Vehicle tester

• Current Pick-Up (V.A.G 1526 B/2)

• Multi-Meter (V.A.G 1526 D)

• Test Instrument Adapter/DSO (5-pin) (VAS 5565)

• The battery voltage and the temperature of the diesel fuel strongly influence the current draw of the fuel pump. Make sure the battery voltage is minimum of 12.5 volts during the test.

• The vehicle must be fueled with diesel fuel treated for the season. Diesel fuel sold in the summer must be able to be filtered down to 0 °C (32 °F) and during the transition time down to -10 °C (14 °F), and in the winter down to -20 °C (-4 °F). Under some conditions, summer diesel fuel can coagulate at low winter temperatures. If not sure, take a sample of the winter fuel and let it stand at low outside temperatures for approximately 1 hour. If the fuel coagulates at temperatures down to -20 °C (-4 °F), then this diesel fuel is not suited for low temperatures. This coagulation can plug the screen in the fuel delivery unit as well as in the fuel filter.

Test Conditions

• Connect the battery charger to make sure the voltage supply is a minimum 12.5 volts

• Diesel fuel temperature is above 10 °C (50 °F)

Test Sequence

- Remove the rear seat bench.

- Remove the flange cover - 1 - using the trim removal wedge (3409) - arrows -.

- Pull on the connector - 1 - without pressing the release to make sure the connection is secure. If the connector was not connected correctly, it could cause a fault.

- Disconnect the connector - 4 -.

- Install the test instrument adapter/DSO (5-pin) (VAS 5565) between the connectors on the fuel delivery unit and cover.

- Connect the current pick-up (V.A.G 1526 B/2) - A - to the red cable, with the words "current clamp" on it, on the test instrument adapter/DSO (5-pin) (VAS 5565).

• The current clamp from the multi-meter (V.A.G 1715) can also be connected to the red wire with the word "current clamp" on it, on the rest instrument adapter/DSO (5-pin) (VAS 5565).

- Turn on the ignition.

- Connect the vehicle diagnostic tester and perform the Guided Function "check electric fuel pump(s)".

• The fuel pump now runs for 30 seconds.

- Read the current draw on the multi-meter (V.A.G 1526 D). Specified value: Max. 14 amperes.

If the measured value lies outside the specified value:

- Remove the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.

- Check the electrical wires between the flange and the fuel pump for continuity.

- Check the filter screen in the bottom of the fuel delivery unit for dirt or to see if it is plugged.

Check for an open circuit or dirt.

- Replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.