Fuel Pump, Checking

Fuel Pump, Checking

• When replacing the fuel delivery unit, check the fuel tank for visible contamination and clean if necessary.

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)

• Measuring Container, 3 Liter

=> [ Function and Voltage Supply, Checking ]

=> [ Fuel Pressure, Checking ]

=> [ Residual Pressure, Checking ]

=> [ Fuel Delivery Rate, Checking ]

=> [ Current Draw, Checking ]

Function and Voltage Supply, Checking

• Battery voltage is at least 11.5 volts

• The fuel pump fuse in the fuse panel is OK.

• The fuel pump control module (J538) is OK

Test Sequence:

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

- Connect the vehicle diagnostic tester as follows:

- Connect the diagnostic cable connector to the Data Link Connector (DLC) in the driver's footwell.

- Turn on the ignition.

- Press the buttons for Vehicle Self-Diagnosis, Engine electronics and Output Diagnostic Test Mode (DTM) one after another on the display.

- Press the right arrow button -> on the display until output Diagnostic Test Mode (DTM) for the fuel pump electronics is reached.

Fuel pump must now accelerate slowly up to maximum RPM.

• The fuel pump runs quietly.

- Turn off the ignition.

If the Fuel Pump Does Not Start:

- Remove the rear seat bench.

- Remove the cover that is on the right side of the fuel tank when viewed in the direction of travel.

- First, pull on the 5 pin connector - 1 - without pressing the release to make sure it is connected securely. If the connector was not connected correctly, check the fuel pump function again.

- Disconnect the connector - 1 -.

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

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

- Connect the multi-meter (V.A.G 1715) to wires - 1 and 6 - on test instrument adapter/DSO (5-pin) (VAS 5565).

- Activate the fuel pump with output DTM.

• The voltage must increase to battery voltage during output DTM.

Voltage Supply Not OK:

- Locate and repair the open circuit in the wiring using the wiring diagram.

Voltage Supply OK:

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

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

If No Open Circuits are Found:

- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.

Fuel Pressure, Checking

Test Conditions:

• The fuel pump function must be checked. Refer to => [ Function and Voltage Supply, Checking ].

Test Sequence:

• Output Diagnostic Test Mode (DTM) checks the fuel pressure.

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 supply line (metal coupling) - 2 - and collect leaking fuel with a cloth.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the adapters (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.

- Check the fuel pressure on the pressure tester.

• Specified value: 4.0 to 7.0 bar

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

If the Specification is Not Obtained:

- Replace the left flange with the pressure relief valve, suction jet pump and fuel filter.

• The pressure relief valve and the fuel filter are integrated in the fuel level sensor 2 (G169) with the suction jet pump and cannot be replaced individually.

- Repeat the test.

If the Specification is Again Not Obtained:

- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.

Residual Pressure, Checking

Test Conditions:

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

Test Sequence:

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

- Check the fuel pressure on the pressure tester.

• Specified value: 4.0 to 7.0 bar

- End the On Board Diagnostic (OBD) and turn off the ignition.

- Watch the pressure decrease 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 mode to build fuel pressure.

- Close the shut-off lever - B - on the pressure tester as soon as the pressure accumulates. 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 fuel pipe to the high pressure pump 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 flange for leaks.

If no problem is found in the outer fuel lines, search for the leak in the fuel tank. Proceed as follows:

- Open the right and left flanges. Make sure all the line connections are connected and not leaking.

If no malfunction can be found:

- First, replace the left flange with the pressure relief valve and fuel filter. Repeat the pressure retention test. If the leak is still present, the check valve in the fuel pump is leaking. Replace the fuel delivery unit.

Fuel Delivery Rate, Checking

Test Conditions:

• The voltage supply is OK.

• If driving is still impaired with the fuel tank 1/4 full, then perform a fuel delivery test with the fuel tank only 1/4 full or with very little fuel in the fuel tank.

- Remove the seat bench.

- Remove the cover that is on the right side of the fuel tank when viewed in the direction of travel.

- First, pull on the 5 pin connector - 1 - without pressing the release to make sure it is connected securely. If the connector was not connected correctly, it could cause a fault.

- Connect the remote control (V.A.G 1348/3A) to the test instrument adapter/DSO (5-pin) (VAS 5565) and to the battery positive (+).

- Disconnect the supply line (metal coupling) - 2 - and collect leaking fuel with a cloth.

• Press in the securing ring to disengage the fuel line.

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

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

Danger of spraying when opening shut-off valve; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.

- Operate the remote control (V.A.G 1348/3A). Slowly close the shut-off lever - arrow - until the pressure tester shows 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. So, connect the multi-meter (V.A.G 1715) to wires - 1 and 5 - of the test instrument adapter/DSO (5-pin) (VAS 5565).

- Operate the remote control for 60 seconds and simultaneously measure voltage on the fuel pump.

- Compare the quantity of fuel delivered with specification.

*) Minimum delivery rate cm3/60 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 1200 cm3/60 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:

- Open the right and left flanges. Make sure all the line connections are connected and not leaking. Check the filter strainer in the fuel delivery unit and fuel tank for contamination.

If no malfunction can be found:

- First, replace the left flange with the pressure relief valve and fuel filter. Repeat the fuel delivery test. If the fuel delivery quantity is still not reached, the fuel pump is faulty. Replace the fuel delivery unit.

Delivery rate has been obtained, but malfunctions are still suspected in the fuel supply (for example, intermittent loss of fuel supply):

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

Current Draw, Checking

- Remove the rear seat bench.

- Remove the cover that is on the right side of the fuel tank when viewed in the direction of travel.

- First, pull on the 5 pin connector - 1 - without pressing the release to make sure it is connected securely. If the connector was not connected correctly, it could cause a fault.

- Disconnect the connector - 1 -.

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

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

- Connect the current clamp - A - to the red wire on the test instrument adapter/DSO (5-pin) (VAS 5565) with the word "current clamp" on it.

- Start the engine and run at idle speed.

- Measure the current draw of the fuel pump.

• Specified value: Max. 16 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 is sporadic, the test can also be performed during a road test, but a second person is required.

If the Current Draw is Exceeded:

- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.