Fuel Pump, Checking

Fuel Pump, 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)

• Voltage Tester (V.A.G 1527 B)

• Vehicle Diagnostic Tester

• Measuring Container, 3 Liter

=> [ Function and Voltage Supply, Checking ]

=> [ Fuel Pressure, Checking ]

=> [ Residual Pressure, Checking ]

Engine Codes CBTA and CBUA => [ Fuel Delivery Volume, Checking ]

Engine Codes CCTA and CBFA => [ Fuel Delivery Volume, 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 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 on the ignition.

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

- Press the right arrow button on the display to initiate fuel pump activation.

The fuel pump must run.

• The fuel pump runs quietly.

- Turn off the ignition.

If the fuel pump does not start up

- Remove the rear seat bench.

- Remove the cover - 1 - from the fuel delivery unit. The arrow - 2 - points in the direction of travel.

- Make sure the connector - arrow - is secure. 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.

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

- Connect a voltage tester (V.A.G 1527 B) to wires - 1 and 5 - on the test instrument adapter/DSO (5-pin) (VAS 5565).

- Turn on the ignition.

• The Light Emitting Diode (LED) must light up briefly.

If the LED does not light up briefly:

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

If the LED lights up briefly (the voltage supply is OK):

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

- Check to see 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

The fuel lines are under pressure.

Danger of personal injury to eyes and skin.

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. Open the connection carefully and release the pressure.

- Disconnect the fuel supply line - 1 - and wipe up any fuel with a cloth. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Service and Repair.

- 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 diagnostic test mode 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 => [ Residual 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 fuel filter. Refer to=> [ Fuel Filter ] 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. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Service and Repair.

- 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.

- Activate the fuel pump with output diagnostic test mode to build fuel pressure.

- Closes the shut off lever - A - slowly. The pressure must increase to a minimum of 7.0 bar. If 7.0 bar is reached, open the shut off lever again immediately!

If the pressure has increased:

- Replace the fuel filter if the fuel pump is OK, but the pressure relief valve in the fuel filter is faulty, refer to => [ Fuel Filter ] Fuel Filter.

If the pressure does not increase:

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

Residual Pressure, Checking

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

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

• 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 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 diagnostic test mode 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 a 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.

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 fuel return line. Proceed as follows:

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

- 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:

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

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, refer to => [ Fuel Filter ] Fuel Filter.

Fuel Delivery Volume, Checking

• 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 rear seat bench.

- Remove the cover - 1 - from the fuel delivery unit. The arrow - 2 - points in the direction of travel.

- 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.

- Connect the remote control (V.A.G 1348/3A) to the test instrument adapter/DSO (5-pin) (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.

- Disconnect the fuel supply line - 1 - and wipe up any fuel with a cloth. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Service and Repair.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the hose (VAS 6550/2). Hold 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 a container in front of the free connection of the 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 the test instrument adapter/DSO (5-pin) (VAS 5565) wires - 1 and 5 -.

- Operate the remote control for 60 seconds while measuring the battery voltage.

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

*) 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 1,200 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:

- Check the filter, perform the following:

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. 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 ] Service and Repair.

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

- The fuel filter is faulty. Replacing, refer to => [ Fuel Filter ] Fuel Filter.

If the minimum delivery rate is again not obtained:

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

- Check the filter screen for dirt.

Only when up to now, no malfunction has been detected:

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

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

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

Fuel Delivery Volume, Checking

Test Conditions:

• The voltage supply is OK.

• The fuel filter is OK.

- Remove the rear seat bench.

- Remove the cover - 1 - and the fuel pump control module (J538) - 2 - 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.

- Disconnect the connector.

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

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

The fuel system is under pressure!

• Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin.

• Before loosening line connections, place a cloth around the connection point. Then release pressure by carefully pulling off the line.

- Disconnect the fuel supply line - 1 - and wipe up any fuel with a cloth. Disconnecting the couplings, refer to => [ Coupling, Disconnecting ] Service and Repair.

- Connect the pressure tester (VAS 6550) to the fuel supply line using the hose (VAS 6550/2). Hold 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 a container in front of the free connection of the pressure measuring device.

- Operate the remote control (V.A.G 1348/3A). Slowly close the shut off lever - arrow - until the pressure gauge shows 4 bar. From this point on do not move position of the shut off lever.

- Empty the measuring container.

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

- Operate the remote control for 60 seconds and simultaneously measure the 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:

- Check the fuel filter as follows:

The fuel system is under pressure!

• Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin.

• Before loosening line connections, place a cloth around the connection point. Then release pressure by carefully pulling off the line.

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

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

- 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.

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 cover - 1 - from the fuel delivery unit. The arrow - 2 - points in the direction of travel.

- 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.

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

- Start the engine and let it run in idle.

- Measure the current draw of the fuel pump.

• Specified value: Max. 10 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 the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.