Fuel Pump, Checking

Fuel Pump, Checking

=> [ Function and Voltage Supply, Checking ]

=> [ Fuel Pressure Regulator and Holding Pressure, Checking ]

=> [ Fuel Delivery Rate, Checking ]

=> [ Current Draw, Checking ]

=> [ Fuel Pump Check Valve, Checking ]

• After removing 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)

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

• Measuring Container, 2 Liter

Function and Voltage Supply, Checking

• The fuel pump relay (J17) is OK

• Battery voltage is at least 11.5 volts

• The fuel pump fuse is OK.

• The output diagnostic test mode 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 the ignition on.

- 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 to initiate fuel pump activation.

The fuel pump must run.

- Turn off the ignition.

If the fuel pump does not start:

- Remove the rear seat bench.

- Remove the cover from the fuel delivery unit.

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

- Disconnect the connector - arrow -.

- Check the contacts on the connector and 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 a multi-meter (V.A.G 1715) to wires - 1 and 5 - of the test instrument adapter/DSO (5-pin) (VAS 5565).

- Start the output diagnostic test mode again and measure the voltage at the fuel pump.

• Specified value: approximately 2 volts less than battery voltage.

Voltage supply is not OK

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

Voltage supply is OK

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 disconnecting a fuel hose. Remove the hose connection carefully to release the pressure.

- Disconnect the fuel lines - 1 and 2 - from the flange. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.

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

- See if the wires between the flange and the fuel pump are connected.

If no open circuits are found

- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit/Fuel Level Sensor ] Service and Repair.

Fuel Pressure Regulator and Holding Pressure, Checking

• The fuel pressure regulator regulates the fuel pressure to approximately 4 bar.

• The fuel pressure regulator is located on the fuel filter. The fuel pressure regulator is integrated into the fuel filter and cannot be replaced separately.

• Follow all safety precautions. Refer to => [ Safety Precautions ] Safety Precautions.

• Follow the guidelines for clean working conditions. Refer to => [ Clean Working Conditions ] Clean Working Conditions.

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. Before loosening the fuel lines, place a cloth around the connection point. Remove the hose connection carefully to release the pressure.

- Disconnect the fuel supply line - 3 -. Pull the pull release upward into the housing to release the line - 3 -.

- 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.

- Start the engine and run at idle speed.

• If the engine does not start, activate the fuel pump using output diagnostic test mode.

- Check the fuel pressure on the pressure tester.

• Specified value: 3.7 to 4.2 bar

If the fuel pressure is OK, check the residual pressure.

If the specification is exceeded:

- Check the fuel return line between the fuel filter and the flange for possible restrictions or blockages.

If no malfunction can be found:

- The fuel pressure regulator is faulty. Replace it.

If the specification is not obtained:

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

If no malfunction can be found:

- Replace the fuel pressure regulator.

• The fuel pressure regulator is integrated into the fuel filter and cannot be replaced separately.

- 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 Level Sensor ] Service and Repair.

If the specification is not reached, check the residual pressure as follows:

- 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:

- Start the engine and run at idle speed.

- Turn the ignition off and close the pressure tester shut off lever - B - immediately.

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 rail and fuel injectors for leaks.

If the pressure drops again:

There is a leak on the fuel tank side.

- Check the fuel lines for leaks.

If no malfunctions are found in the fuel lines:

- Test the check valve in the fuel pump. Refer to => [ Fuel Pump Check Valve, Checking ].

If no malfunction is found here either:

- Replace the fuel filter. Refer to => [ Fuel Filter ] Fuel Filter.

• The fuel pressure regulator is integrated into the fuel filter and cannot be replaced separately.

- Bleed the fuel system.

Fuel Delivery Rate, Checking

• The voltage supply is OK.

• The fuel pressure regulator and holding pressure are OK. Checking, refer to => [ Fuel Pressure Regulator and Holding Pressure, Checking ]

• The fuel filter is OK.

- Remove the rear seat bench.

- Remove the cover from the fuel delivery unit.

- First, pull on the connector - arrow - without pressing the retainer 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 battery positive (+).

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

• The fuel pump delivery rate is measured at 4 bar. Check the fuel pressure before measuring the delivery quantity. Refer to => [ Fuel Pressure Regulator and Holding Pressure, Checking ].

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 disconnecting a fuel hose. Remove the hose connection carefully to release the pressure.

- Disconnect the return line - 1 - from the fuel pressure regulator. Disconnecting couplings, refer to => [ Coupling, Disconnecting ] Coupling, Disconnecting.

• Press the locking ring to unlock the fuel line.

- Connect the hose (VAS 6550/1) to the fuel pressure regulator and hold the other end of the hose in a measuring container.

- Operate the remote control (V.A.G 1348/3A) approximately 5 seconds to fill the fuel filter.

- Empty the measuring container.

- The fuel pump delivery rate depends on the voltage. 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 30 seconds and measure the voltage.

- Compare the quantity of fuel delivered with specification.

*) 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 580cm3/30 s.

If the specification is not obtained:

- Check the supply line to the filter for possible restrictions (kinks) or clogging.

If the fuel line is OK:

- 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 as follows:

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 disconnecting a fuel hose. Remove the hose connection carefully to release the pressure.

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

- Connect the pressure tester (VAS 6550) to the fuel supply line using the hose (VAS 6550/1). Hold the other 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). Slowly close the shut off lever - A - 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 fuel strainer for contamination.

Only when up to now no malfunction has been detected:

- Replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit/Fuel Level Sensor ] Service and Repair.

- Reconnect all disconnected fuel lines.

- Bleed the fuel supply system.

If the 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 fuel delivery unit cover.

With a fuel pump control module (J538)

- Remove the cover - 1 - with the fuel pump control module - 2 - from the fuel delivery unit.

Continuation for All

- First, pull on the connector - arrow - without pressing the retainer to make sure it connected securely. If the connector was not connected correctly, it could cause a fault.

- Disconnect the connector - arrow -.

- 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 fuel delivery unit and cover.

- Connect the current clamp - A - to the red wire of 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. 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:

- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit/Fuel Level Sensor ] Service and Repair.

Fuel Pump Check Valve, Checking

- Remove the rear seat bench.

- Remove the cover from the fuel delivery unit.

- First, pull on the connector - arrow - without pressing the retainer to make sure it 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 battery positive (+).

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 disconnecting a fuel hose. Remove the hose connection carefully to release the pressure.

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

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

- Close the shut off lever - A - on the pressure tester (VAS 6550) so the lever is perpendicular to the direction of flow.

- Operate the remote control at short intervals, until a pressure of approximately 4 bar has built up.

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

- If pressure builds up too high, lower the excess pressure by carefully opening the shut off lever.

- Watch the pressure decrease on the pressure tester. After 10 minutes the pressure must not drop below a 3 bar decrease.

If the pressure drops further:

- Check the line connections for leaks.

If no fault is detected in the wiring:

- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit/Fuel Level Sensor ] Service and Repair.