Fuel Pump, Checking

Fuel Pump, 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, 3 Liter

=> [ Function and Voltage Supply, Checking ]

=> [ Fuel Pressure, Checking ]

=> [ Residual Pressure, Checking ]

=> [ Delivery Quantity, Checking ]

=> [ Current Draw, Checking ]

Function and Voltage Supply, Checking

• Battery voltage at least 11.5 volts.

• Fuel pump fuse in the fuse panel is OK.

• Fuel pump control module (J538) is OK

Test Sequence:

• The output diagnostic test mode checks the fuel pump.

- Connect the vehicle diagnostic tester as follows:

- Connect the diagnostic cable - 2 - to the Data Link Connection (DLC) 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 until output diagnostic test mode of fuel pump electronics.

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 bench seat.

- Disconnect the connector - arrow - from the fuel pump control module.

- Using the multi-meter (V.A.G 1715) , check the voltage supply between terminals - 1 and 6 -.

• Specified value: approximately battery voltage

Voltage Supply is not OK:

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

Voltage Supply is OK:

- Remove the cover - 2 - and the fuel pump control module - 2 - 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.

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 lines - 1 and 2 - from the flange.

• Press in the securing rings to disengage the lines.

- 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:

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

Fuel Pressure, Checking

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

• Output diagnostic test mode activates the fuel pump.

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 - 2 -. Push the locking ring upward and into the housing.

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

- 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.

- 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 Exceeded:

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

If no malfunction can be found:

- Replace the fuel filter, the pressure relief valve inside the fuel filter is faulty.

If the Specification is not Obtained:

- Check the fuel pressure before the fuel filter as follows:

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

- Using the hoses (VAS 6550/1) and (VAS 6550/2) , connect the pressure tester (VAS 6550) between the fuel filter and fuel supply line.

- 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 diagnostic test mode.

- Close the shut off lever - A - while the fuel pump is running.

• Pressure must increase to a min. 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, the fuel pump is OK but the pressure relief valve in the fuel filter is faulty.

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

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

Test Sequence:

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

- Check the fuel pressure on the pressure tester.

• Specified value: 4.0 to 7.0 bar

- End the output diagnostic test mode 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 diagnostic test mode to build fuel pressure.

- Close the shut off lever - B - on the pressure tester as soon as pressure accumulates. The lever is perpendicular to the direction of flow.

If 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 Side Fuel Pressure, Releasing ] Service and Repair.

If the pressure drops again:

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

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

If no malfunctions are found on fuel line:

- Check the pressure retention valve in the fuel delivery unit. Proceed as follows:

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

- Using the hoses (VAS 6550/1) and (VAS 6550/2) , connect the pressure tester (VAS 6550) between the fuel filter and fuel supply line.

- 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:

- 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.

Delivery Quantity, Checking

Test Conditions:

• Voltage supply is OK.

• Fuel filter is OK.

- Remove the bench seat.

- 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 is 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 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 - 2 -. Push the locking ring upward and into the housing.

- Connect the pressure tester (VAS 6550) and the hose (VAS 6550/2) to the fuel supply line. 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 the 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 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 connectors - 1 and 5 - of 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 the 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 for 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) and the hose (VAS 6550/1) to the fuel supply line. Hold the other end of 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 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 bench seat.

- Remove the cover - 2 - and 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 is connected securely. If the connector was not connected correctly, it could cause a fault.

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

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