Fuel Pump, Checking
Fuel Pump, Checking
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Pressure, Checking ]
=> [ Residual Pressure, Checking ]
=> [ Fuel Delivery, Checking ]
=> [ Current Draw, 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
Read the safety precautions before starting. Refer to => [ Safety Precautions ] Fuel Supply.
Test Conditions
• Battery voltage is at least 11.5 volts.
• The fuel pump fuse is OK.
• The fuel pump control module is OK.
• The low fuel pressure sensor is OK.
Test Sequence
• 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 until the output diagnostic test mode of fuel pump electronics.
The 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:
- Remove the rear seat bench.
- Disconnect the connector from the fuel pump control module.
- Check the voltage supply between terminals - 1 and 6 - using the multi-meter (V.A.G 1715) or equivalent.
• Specified value: approximately battery voltage
If the voltage supply is not OK:
- Locate and repair the open circuit in the wiring using the wiring diagrams.
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.
- 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 locking ring to unlock the fuel line.
- 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 Delivery Unit.
Fuel Pressure, Checking
Test Conditions
• The fuel pump function must be checked.
Test Sequence
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 wipe up any leaking fuel with a cloth.
• Press the locking ring to unlock the fuel line.
- 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.
- 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 specification is exceeded:
- The pressure relief valve in the fuel filter is faulty, replace the flange with fuel filter:
• Vehicles with Front Wheel Drive (FWD), see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
• Vehicles with All Wheel Drive (AWD), see - item 22 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
If the specification is not obtained:
- Check the fuel lines for possible restrictions (kinks) or blockages.
If no malfunction can be found:
- Replace the flange with fuel filter and pressure relief valve:
• Vehicles with FWD, see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
• Vehicles with AWD, see - item 22 - 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.
Residual Pressure, Checking
Test Conditions
• The fuel pressure is OK and the pressure tester (VAS 6550) is connected.
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 the pressure no longer drops:
• 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 line 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 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 and repeat the pressure retention test. If the leak is still present, replace the fuel delivery unit.
• Vehicles with FWD, see - item 20 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
• Vehicles with AWD, see - item 22 - in the => [ Fuel Tank and Attachments Overview ] Fuel Tank and Attachments Overview.
Fuel Delivery, Checking
Test Sequence
- 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.
- 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 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 wipe up any leaking fuel with a cloth.
• Press the locking ring to release the fuel lines.
- 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 levers are open.
Danger of spraying when opening the shut off lever; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold the container in front of the open connection of the pressure tester.
- Operate 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 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) , or equivalent, to wires - 1 and 5 - of the test instrument adapter/DSO (5-pin) (VAS 5565).
- Operate the remote control for 30 seconds and simultaneously measure the voltage of the fuel pump.
- Compare the quantity of fuel delivered with the specification.
*) Minimum delivery rate cm3/30 s
**) Voltage on 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 580 cm3/30 s.
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.
- 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
Test Sequence
- 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.
- 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 test instrument adapter/DSO (5-pin) (VAS 5565) red wire 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. 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.