Fuel Pump, Checking

Fuel Pump, Checking

=> [ Function and Voltage Supply, Checking ]

=> [ Fuel Pressure, Checking ]

=> [ Holding Pressure, Checking ]

=> [ Fuel Delivery Quantity, Checking ]

=> [ Current Draw, Checking ]

Special tools, testers and auxiliary items required

• Pressure Tester (VAS 6550)

• Remote Control (V.A.G 1348/3A)

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

• Multi-meter (V.A.G 1715)

• Wrench (T10202)

• Torque Wrench (40-200 Nm) (V.A.G 1332)

• Measuring Container, 2 Liter

Function and Voltage Supply, Checking

Test Conditions

• The battery voltage is at least 11.5 volts

• The fuel pump control module fuse is fuse OK

• The fuel pump control module is OK

Test Sequence

• The output Diagnostic Test Mode (DTM) checks the fuel pump.

- Connect the vehicle diagnostic tester - 1 - as follows:

- Connect the diagnostic cable - 2 - connector to the diagnostic connection inside the drivers foot well.

- Turn on the ignition.

- On the OBD screen, press one button after the other: 01 - engine electronics and output diagnostic test mode.

- Push the arrow button on the display to the fuel pump electronics output DTM.

The fuel pump must now accelerate slowly up to maximum speed.

• The fuel pump runs quietly.

- Turn off the ignition.

If the Fuel Pump does not Start Up

- Remove the rear seat bench.

- Disconnect the connector from the fuel pump control module.

- Check the voltage supply between the terminal - 1 and 6 - using the multi-meter (V.A.G 1715).

• Specified value: approximately battery voltage

Voltage Supply is not OK

- Locate and repair the open circuit in the wiring.

Voltage Supply is OK

- Remove the cover for the fuel delivery unit.

- Make sure the connector - arrow - is secure. Pull on the connector without pressing the catch. Repeat the fuel pump functionality test if the connector was not connected correctly.

- Disconnect the connector - arrow -.

- Check the contacts on the connector and on the fuel delivery unit for damage.

The fuel supply line is under pressure. Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.

- Disconnect the fuel lines - 1 and 2 - from the flange.

• Press the locking ring to release the fuel lines.

- Remove the lock ring using the wrench (T10202).

- Check if the electrical wiring between the flange and fuel pump is connected.

If No Open Circuits are Found

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

Fuel Pressure, Checking

• Output Diagnostic Test Mode (DTM) activates the fuel pump.

The fuel supply line is under pressure. Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.

Test Sequence

- Disconnect the fuel supply line (metal coupling) - arrow - and absorb the leaking fuel with a clean cloth.

• Press the locking ring to unlock the fuel line.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the hoses (VAS 6550/1) and (VAS 6550/2).

- Make sure the drain is closed and the shut off levers are open.

- Activate the fuel pump with output DTM to build fuel pressure.

- Read the fuel pressure.

• Specified value: 4.0 to 7.0 bar.

If the fuel pressure is OK, check the residual pressure. Refer to => [ Holding Pressure, Checking ].

If the Specification is Exceeded

- Check the return line between the fuel filter and the fuel pump for kinks or blockages.

If no malfunction can be found:

- The pressure relief valve in the fuel filter is malfunctioning, replace the fuel filter.

If the Specification is Not Obtained

- Check the fuel pressure in front of the fuel filter as follows:

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

- Connect the pressure tester (VAS 6550) between the fuel filter and fuel supply line using the hoses (VAS 6550/1) and (VAS 6550/2).

- Make sure the drain is closed and the shut off levers are open.

- Turn on the ignition and actuate the fuel pump using the output DTM.

- Close the shut off lever - A - while the fuel pump is running. The pressure must increase to a minimum of 7.0 bar. If 7.0 bar is reached, open the shut off lever again immediately!

- Replace the fuel filter if the fuel pump is OK but the pressure relief valve in the fuel filter is faulty.

If the pressure does not increase:

- Replace the fuel delivery unit, refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit. The fuel pump is faulty.

Holding Pressure, Checking

• The fuel pressure is OK and the pressure tester (VAS 6550) is connected. Fuel pressure checking. Refer to => [ Fuel Pressure, Checking ].

Test Sequence

- Activate the fuel pump with output Diagnostic Test Mode (DTM) to build fuel pressure.

- Read the fuel pressure.

• Specified value: 4.0 to 7.0 bar

- Observe the pressure drop on the pressure tester. After 10 minutes the pressure must not drop below a 3.0 bar decrease.

If the pressure drops further:

- Activate the fuel pump with output DTM to build fuel pressure.

- Close the shut off lever - B - on the pressure tester immediately after the pressure has been reached. The lever is perpendicular to the direction of flow.

If the Pressure No Longer Drops Now

• Check for the leak on the engine side. Repeat the residual pressure check. Close the shut off lever - A - this time to determine if there actually is a leak on the engine side.

- Check the high pressure pump fuel pipe for leaks.

If no malfunction can be found:

- Replace the high pressure pump, refer to => [ High Pressure Pump ] High Pressure Pump.

If the Pressure Drops Again

Check for the leak on the fuel tank side. Proceed as follows:

- Check the fuel line to the fuel filter for leaks.

If no malfunctions are found with the fuel line:

- Check the pressure retention valve in the fuel return line, as follows:

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

- Connect the pressure tester (VAS 6550) between the fuel filter and fuel supply line using the hoses (VAS 6550/1) and (VAS 6550/2).

- Observe the pressure drop on the pressure tester. After 10 minutes the pressure must not drop below a 3.0 bar decrease.

If the pressure drops:

- Replace the fuel delivery unit, refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit. The pressure retaining valve in the fuel pump is defective.

If the pressure does not drop:

- The pressure retention valve in the fuel pump is OK. The pressure relief valve in the fuel filter is faulty. Replace the fuel filter.

Fuel Delivery Quantity, Checking

- Remove the rear seat bench.

- Remove the cover for the fuel delivery unit.

- Make sure the connector - arrow - is secure. Without pressing on the release, pull on the connector. If the connector was not connected correctly, it could cause a fault.

- Disconnect the connector - arrow -.

- Check the contacts on the connector and on the fuel delivery unit for damage.

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

- Connect the remote control (V.A.G 1348/3A) to the adapter (VAS 5565) and to the battery positive (+) terminal inside the engine compartment.

• This step allows the fuel pump to run when the engine is not running.

The fuel supply line is under pressure. Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.

- Disconnect the fuel supply line (metal coupling) - arrow - and absorb the leaking fuel with a clean cloth.

• Press the locking ring to release the fuel lines.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the hoses (VAS 6550/1) and (VAS 6550/2). Hold the other end of the hose (VAS 6550/1) in a measuring container.

- Make sure the drain is closed and the shut off levers are open.

Danger of spraying. Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Hold container in front of the free connection of pressure measuring device.

- Operate the remote control (V.A.G 1348/3A). Close the shut off lever - arrow - slowly until the pressure tester reads 4 bar. From this point on do not move the position of the shut off lever.

- Empty the measuring container.

- The fuel delivery rate of the fuel pump is dependent on battery voltage. Therefore, additionally, connect the multi-meter (V.A.G 1715) to leads - 1 and 5 - of the test instrument adapter/DSO (5-pin) (VAS 5565).

- Operate the remote control for 30 seconds while measuring the battery voltage.

- Compare the delivered quantity of fuel with the specified value.

*) Minimum delivery rate cm3/30 s

**) Voltage on the fuel pump with engine running in idle and the pump is on.

Example:

During the test, a voltage of 10.5 volts is measured. This results in a minimum delivery quantity of approximately 580 cm3/30 s.

If the Specification is Not Obtained

- Check the fuel lines for possible restrictions (kinks) or blockages.

If no malfunction can be found:

- Remove the cap from the fuel filler neck and repeat the test. If the fuel delivery quantity is now reached, check the fuel tank ventilation.

If the Specification is Again Not Obtained

- Check the fuel filter.

The fuel supply line is under pressure. Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Wrap a cloth around the connection before removing a fuel hose. Remove the hose connection carefully to release the pressure.

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

- Connect the pressure tester (VAS 6550) to the fuel supply line using the hoses (VAS 6550/1) and (VAS 6550/2). Hold the other end of the hose (VAS 6550/2) in the measuring container.

- Make sure the drain is closed and the shut off levers are open.

- Operate the remote control (V.A.G 1348/3A). Close the shut off lever - arrow - slowly until the pressure tester reads 4 bar. From this point on do not move the position of the shut off lever.

- Empty the measuring container.

- Repeat the fuel delivery test.

If the minimum delivery rate is now obtained:

- Replace the fuel filter.

If the minimum delivery rate is again not obtained:

- Remove the fuel delivery unit and check the filter screen for dirt.

Only when up to now no malfunction has been detected:

- Replace the fuel delivery unit.

If the fuel delivery rate was reached, even though a fault in the fuel supply is still suspected (for example, intermittent loss of fuel supply):

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

Current Draw, Checking

- Remove the rear seat bench.

- Remove the cover for the fuel delivery unit.

- Make sure the connector - arrow - is secure. Without pressing on the release, pull on the connector. If the connector was not connected correctly, it could cause a fault.

- Connect the current clamp - A - to the red cable labeled "current probe" on the test instrument adapter/DSO (5-pin) (VAS 5565).

- Start the engine and let it idle.

- Measure the current draw of the fuel pump.

• Specified value: Max. 9 amps.

• The fuel pump starting current may be higher than the specified value briefly when starting the engine.

• If the malfunction in the fuel system only occurs sporadically, the test can also be performed during a road test. A second person is needed to do this.

If the current draw is exceeded:

- The fuel pump is faulty. Replace fuel delivery unit, refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.