Engine MFI
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, 2 Liter
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Pressure, Checking ]
=> [ Residual Pressure, Checking ]
=> [ Fuel Delivery, Checking ]
=> [ Current Draw, Checking ]
Function and Voltage Supply, Checking
Conditions
• Battery voltage at least 11.5 volts.
• Fuel pump control module (J538) fuse is OK
• Fuel pump control module is OK
Sequence
• Fuel pump function is checked via output Diagnostic Test Mode (DTM).
- Connect the vehicle diagnostic tester - 1 - as follows:
- Connect diagnostic cable - 2 - to the Data Link Connector (DLC) in the driver's footwell.
- Turn on the ignition.
- Press the Vehicle Self-Diagnosis, Engine Electronics and Output Diagnostic Test Mode buttons on the display.
- Press the right arrow button on the display until output Diagnostic Test Mode (DTM) of fuel pump electronics.
Fuel pump must now accelerate slowly up to maximum RPM.
• Fuel pump runs quietly.
- Turn off the ignition.
If the Fuel Pump Does Not Start
- Remove the rear seat bench.
- Disconnect the connector from the fuel pump control module (J538).
- Check the voltage supply between terminals - 1 and 6 - using (V.A.G 1715).
• Specified value: approximately battery voltage
Voltage Supply Not OK
- Locate and repair the open circuit in the wiring, refer to the.
Voltage Supply OK
- Remove the cover - 1 - with the fuel pump control module (J538) - 2 - from the fuel delivery unit.
- First gently pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. If the connector was not connected correctly, check the fuel pump function again.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
CAUTION!
The fuel system is under pressure!
• Wear protective goggles and protective clothing to prevent injuries and contact with skin.
• Before disconnecting the connection, place a cloth around the connection. Then release pressure by carefully disconnecting the connection.
- Remove the fuel lines - 1 and 2 - from the flange.
• Press in the securing ring to disengage the fuel lines.
- Remove the locking ring using (T10202).
- Check whether the electrical wires between the flange and fuel pump are connected.
If No Open Circuits are Found
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
Fuel Pressure, Checking
CAUTION!
The fuel system is under pressure!
• Wear protective goggles and protective clothing to prevent injuries and contact with skin.
• Before disconnecting the connection, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the supply line (metal coupling) - arrow - and collect any leaking fuel in a cloth.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut off valves are open.
- Activate the fuel pump with output Diagnostic Test Mode (DTM) to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• 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 fuel pump for kinks and/or blockages.
If no malfunction can be found:
- Pressure relief valve in the fuel filter is malfunctioning, replace the fuel filter.
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.
- Connect the (VAS 6550) between the fuel filter and fuel supply line using (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut off valves are open.
- Start the engine and run at idle speed.
- Slowly close the shut off valve - A -. Pressure must increase to a min. 7.0 bar. If 7.0 bar is reached, open the shut off valve again immediately!
If pressure has increased:
- Replace the fuel filter if the fuel pump is OK but the pressure relief valve in the fuel filter is faulty.
If pressure does not increase:
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
Residual Pressure, Checking
• Fuel pressure is OK and the (VAS 6550) is connected. Checking the fuel pressure, refer to => [ Fuel Pressure, Checking ].
Sequence
- Activate the fuel pump with output Diagnostic Test Mode (DTM) to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• Target value: 4.0 to 7.0 bar
- Watch the pressure decrease on the (VAS 6550). 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 valve - B - on the (VAS 6550) as soon as pressure accumulates. The level 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 valve - A - this time to determine if there actually is a leak on the engine side.
- Check the fuel pipe to high pressure fuel pump for leaks.
If no malfunction can be found:
- Replace the high pressure fuel pump. Refer to => [ High Pressure Fuel Pump ] High Pressure Fuel Pump.
If The Pressure Drops Again
Check for the leak on the fuel tank side. Proceed as follows:
- Check the fuel line to 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.
- Connect the (VAS 6550) between the fuel filter and fuel supply line using adapter (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut off valves are open.
- Activate the fuel pump with output DTM to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• Target value: 4.0 to 7.0 bar
- Close the shut off valve - A - once pressure has increased.
- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the pressure drops:
- If the pressure retention valve in the fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
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, Checking
- Remove the rear seat bench.
- Remove the cover - 1 - with the fuel pump control module (J538) - 2 - from the fuel delivery unit.
- First gently pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. 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 (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the (V.A.G 1348/3A) to the adapter (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.
CAUTION!
The fuel system is under pressure!
• Wear protective goggles and protective clothing to prevent injuries and contact with skin.
• Before disconnecting the connection, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the supply line (metal coupling) - arrow - and collect any leaking fuel in a cloth.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/2). Hold the other end of (VAS 6550/1) in a measuring container.
- Make sure the drain is closed and the shut off valves are open.
CAUTION!
Danger of spraying. Wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold the container in front of free connection of the pressure measuring device.
- Operate the (V.A.G 1348/3A). Slowly close the shut off valve - arrow - until the (VAS 6550) shows 4 bar. From this point on do not move the position of the shut off lever.
- Empty the measuring container.
- Fuel delivery rate of the fuel pump is dependent on battery voltage. So, connect the (V.A.G 1715) to connectors - 1 and 5 - on the (VAS 5565).
- Operate the (V.A.G 1348/3A) for 30 seconds and simultaneously measure voltage at the fuel pump.
- Compare the quantity of fuel delivered with specification.
*) Minimum delivery rate cm3/30 s
**) Voltage at 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 as follows:
CAUTION!
The fuel system is under pressure!
• Wear protective goggles and protective clothing to prevent injuries and contact with skin.
• Before disconnecting the connection, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the fuel supply line - arrow - from the fuel filter.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/1). Hold the other end of the adapter (VAS 6550/2) in a measuring container.
- Make sure the drain is closed and the shut off valves are open.
- Operate the (V.A.G 1348/3A). Slowly close the shut off valve - arrow - until the (VAS 6550) 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 fuel strainer for contamination.
Only when up to now no malfunction has been detected:
- 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 - 1 - with the fuel pump control module (J538) - 2 - from the fuel delivery unit.
- First gently pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. 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 (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the current clamp - A - to the red wire with the word "current clamp" on the (VAS 5565).
- Start the engine and run at idle speed.
- Measure the current draw of the fuel pump.
• Specified value: maximum 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 if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.