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)
• Torque Wrench (40-200 Nm) (V.A.G 1332)
• Measuring Container, Minimum 3 Liters
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Pressure, Checking ]
=> [ Holding Pressure, Checking ]
=> [ Fuel Delivery Rate, Checking ]
=> [ Current Draw, Checking ]
Function and Voltage Supply, Checking
• The battery voltage is at least 11.5 volts.
• The fuel pump fuse in the fuse panel is OK.
• The fuel pump control module is OK.
• The output Diagnostic Test Mode (DTM) 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 until the output DTM for the fuel pump electronics is reached.
The 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.
- Disconnect the connector - arrow - from the fuel pump control module.
- Check the voltage supply between terminals - 1 and 6 - using the multi-meter (V.A.G 1715).
• Specified value: approximately battery voltage
If the Voltage Supply is Not OK
- Locate and repair the open circuit in the wiring.
If the Voltage Supply is OK
- Remove the cover - 1 - and the fuel pump control module - 2 - from the fuel delivery unit.
- First, pull on the connector - A - 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 - A -.
- Check the contacts on the connector and the fuel delivery unit for damage.
The fuel supply line is under pressure. Always wear protective eye wear 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 fuel line - B - from the flange.
• Press the lock to unlock the fuel line.
- Remove the lock ring using 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 Delivery Unit.
Fuel Pressure, Checking
Conditions
• The fuel pump function must be checked.
Sequence
• The output Diagnostic Test Mode (DTM) checks the fuel pressure.
Read the safety precautions before starting. Refer to => [ Safety Precautions ] Fuel Supply.
- Pay attention to the rules of cleanliness. Refer to => [ Clean Working Conditions ] Fuel Supply.
The fuel supply line is under pressure. Always wear protective eye wear 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) - arrow - and catch any leaking fuel with a cloth.
• Press the lock ring to unlock the fuel line.
- 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 valves are open.
- Activate the fuel pump with the output DTM to build the 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.
If the Specified Value Is Exceeded
- The pressure relief valve in the flange malfunctioning, replace the flange with fuel filter, see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
If the Specified Value Is Not Obtained
- Check the fuel lines for possible restrictions (kinks) or blockages.
If no malfunction can be found:
- Replace the flange with the fuel filter and pressure relief valve, see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
- Repeat the test.
If the Specified Value Is Again Not Obtained
- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
Holding Pressure, Checking
Conditions
• The fuel pressure is OK and the pressure tester (VAS 6550) is connected. Checking the fuel pressure.
Sequence
- Activate the fuel pump with the output Diagnostic Test Mode (DTM) to build the 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 the output DTM to build the fuel pressure.
- Close the shut off valve - 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 valve - A - this time to determine if there is 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 (- item 1 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview) to the flange for leaks.
If no malfunctions are found with the fuel line:
The pressure relief valve in the flange or pressure retention valve in the fuel pump leaks.
- Replace the flange with the fuel filter, see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview. and repeat the pressure retention test. If the leak is still present, replace the fuel delivery unit.
Fuel Delivery Rate, Checking
Conditions
• The fuel level inside the fuel tank is above reserve.
Sequence
- Remove the rear seat bench "Rear Seats" in
- Remove the cover - 1 - and the fuel pump control module - 2 - from the fuel delivery unit.
- First, pull on the connector - A - 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 - A -.
- 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 to battery positive (+).
• This step allows the fuel pump to run when the engine is not running.
The fuel supply line is under pressure. Always wear protective eye wear 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) - arrow - and catch any leaking fuel with a cloth.
• Press the lock ring to release 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 valves are open.
Danger of spraying when opening the shut off valve; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold a container in front of the open connection of the pressure tester.
- Operate the remote control (V.A.G 1348/3A). Slowly close the shut off valve - arrow - until the pressure tester shows 4 bar. From this point on do not move the position of the shut off valve.
- Empty the measuring container.
- The fuel delivery rate of the fuel pump is dependent on battery voltage. So, also connect the multi-meter (V.A.G 1715) to connections - 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 of the fuel pump.
- Compare the quantity of fuel delivered with the specification.
*) Minimum delivery rate cm3/60 seconds.
**) Voltage of the fuel pump with the 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 seconds.
If the Specification Is Not Obtained
- Check the fuel line for possible restrictions (kinks) or clogging.
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
- Remove the fuel delivery unit and check the fuel strainer for contamination.
- If there is no malfunction here as well, replace the flange with fuel filter, see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
- 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 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.
Current Draw, Checking
- Remove the rear seat bench.
- Remove the cover - 1 - and the fuel pump control module - 2 - from the fuel delivery unit.
- First, pull on the connector - A - 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 - A -.
- 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 words "current clamp" on it.
- Start the engine and run at idle speed.
- 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:
- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.