Fuel Pump, Checking
Fuel Pump, Checking
--> [ Function and Voltage Supply, Checking ]
--> [ Delivery Quantity, Checking ]
--> [ Current Draw, Checking ]
--> [ Fuel Pump Check Valve, Checking ]
Special tools, testers and auxiliary items required
• Wrench (3087) or wrench (T10202)
• Fuel injector pressure gauge (VAG 1318)
• Pressure gauge adapter (VAG 1318/1)
• Adapter (VAG 1318/11)
• Adapter set (VAG 1318/17)
• Torque wrench 40-200 Nm (VAG 1332)
• Remote control (VAG 1348/3A)
• Test instrument adapter/DSO (5 pin) (VAS 5565)
• Voltage tester (VAG 1527B)
• Measuring container
Function and Voltage Supply, Checking
• Battery voltage at least 11.5 V
• Fuse for the fuse pump on the fuse holder is OK.
• Fuel pump function is checked via the output Diagnostic Test Mode (DTM).
- Connect the (VAS 5051) as follows:
- Connect the diagnostic cable connector to the Data Link Connector (DLC) in the driver's footwell.
- Turn on the ignition.
- Press the buttons for "Vehicle Self-Diagnosis", " 01 - Engine electronics" and "Output Diagnostic Test Mode (DTM) " on display in succession.
- Press the right arrow button on the display to initiate fuel pump activation.
Fuel pump must run.
• Fuel pump runs quietly.
- Switch off ignition.
If the Fuel Pump Does Not Start Up
- Remove the rear seat bench.
- Unclip the cover - 1 - from the fuel delivery unit. Arrow - 2 - points in direction of vehicle travel.
- Disconnect the electrical connector - 1 -.
- Install the (VAS 5565) to the electrical connector on the cover and the fuel delivery unit.
- Connect the (VAG 1527B) to the wires - 1 - and - 5 - on the (VAS 5565).
- Switch the ignition on.
• 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.
LED lights up briefly (voltage supply OK):
- Remove the fuel delivery unit. Refer to --> [ Fuel Delivery Unit ] .
- Check if the electrical wiring between the flange and fuel pump is connected.
If no open circuits are found:
- Fuel pump is faulty, replace the fuel delivery unit. Refer to --> [ Fuel Delivery Unit ] .
Delivery Quantity, Checking
• Voltage supply OK.
• Fuel pressure regulator and residual pressure OK. Refer to --> [ Fuel Pressure Regulator and Residual Pressure, Checking ] .
• Fuel filter OK.
- Remove the fuel filler cap from the fuel filler tube.
- Remove the rear seat bench.
- Unclip the cover - 1 - from the fuel delivery unit. Arrow - 2 - points in direction of vehicle travel.
- Disconnect the electrical connector - 1 - from the fuel delivery unit.
- Install the (VAS 5565) to the electrical connector on the cover and on the fuel delivery unit.
- Connect the (VAG 1348/3A) to the (VAS 5565) and to the positive (+) side of the battery.
• Delivery rate of the fuel pump is measured at 4 bar. Therefore, measure the fuel pressure before measuring the delivery rate. Refer to --> [ Fuel Pressure Regulator and Residual Pressure, Checking ] .
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the return line - 1 - from fuel filter/pressure regulator.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAG 1318/17) to the fuel filter/pressure regulator and hold the end of the (VAG 1318/17) in a measuring container.
- Operate the (VAG 1348/3A) approximately 5 seconds in order to fill the fuel filter.
- Empty the measuring container.
- Delivery rate of the fuel pump is dependent on voltage. Therefore connect a multi-meter to the battery.
- Operate the (VAG 1348/3A) for 30 seconds and measure battery voltage.
- Compare the quantity of fuel delivered with the specification table.
*) Minimum delivery rate cm3/30 s
**) Voltage at fuel pump with engine off and pump running (approximately 2 Volts less than battery voltage).
Example:
During the test, a voltage of 12.5 volts is measured at the battery. Since the voltage at the pump is approximately 2 volts less than battery voltage, there is a minimum delivery rate of 580 cm3/30 s.
If the Minimum Delivery Rate is Not Attained
- Check the supply line to the filter for possible restrictions (kinks) or clogging.
If the fuel line is OK:
- Check the fuel delivery rate in front of the fuel filter.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the supply line - 1 - from the fuel filter.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAG 1318) to the (VAG 1318/17) as shown.
- Connect the (VAG 1318/1) to the (VAG 1318/11) of the (VAG 1318) and hold the other end in a measuring container.
CAUTION!
Danger of spraying when opening shut off valve! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.
- Open the shut off valve of the (VAG 1318). Lever will point in direction of flow - A -.
- Operate the (VAG 1348/3A). Slowly close the shut off tap, until the (VAG 1318) shows 4 bar. From this point on do not move the position of the shut off tap.
- Empty the measuring container.
- Operate the (VAG 1348/3A) again for 30 seconds. Compare the delivery rate with the value determined from the first measurement.
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 filter strainer for dirt.
Only when up to now, no malfunction has been detected:
- Replace the fuel delivery unit. Refer to --> [ Fuel Delivery Unit ] .
- Reconnect all disconnected fuel lines.
- Bleed the fuel system. Refer to --> [ Fuel System, Bleeding ] .
Delivery rate has been obtained, but malfunctions are still suspected in the fuel supply, for example sporadic loss of fuel supply:
- Check the fuel pump current draw. Refer to --> [ Current Draw, Checking ].
Current Draw, Checking
- Remove the rear seat bench.
- Unclip the cover - 1 - from the fuel delivery unit. Arrow - 2 - points in direction of vehicle travel.
- Disconnect the electrical connector - 1 -.
- Install the (VAS 5565) to the electrical connector on the cover and on the fuel delivery unit.
- 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: max. 9 amps.
• If the malfunction in the fuel system is sporadic, test can also be performed during a road test, but a second person is required.
If the current draw is exceeded:
- Fuel pump faulty, replace the fuel delivery unit. Refer to --> [ Fuel Delivery Unit ] .
Fuel Pump Check Valve, Checking
- Remove the rear seat bench.
- Unclip the cover - 1 - from the fuel delivery unit. Arrow - 2 - points in direction of vehicle travel.
- Disconnect the 5 pin electrical connector from the fuel delivery unit.
- Install the (VAS 5565) to the electrical connector on the cover and on the fuel delivery unit.
- Connect the (VAG 1348/3A) to the (VAS 5565) and to positive (+) terminal of the battery.
CAUTION!
Fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before loosening the fuel lines, place a cloth around the connection point. Then release pressure by carefully disconnecting the connection.
- Disconnect the supply line - 1 - from the fuel filter.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAG 1318) to the (VAG 1318/17) as shown.
- Connect the (VAG 1318/1) to the (VAG 1318/11) of the (VAG 1318) and hold the other end in a measuring container.
- Close the shut-off valve of the (VAG 1318) (lever perpendicular to direction of flow, position - B -).
- Operate the (VAG 1348/3A) at short intervals, until a pressure of approximately 4 bar has built up.
CAUTION!
Danger of spraying when opening the shut off valve; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.
- If pressure builds up too high, lower excess pressure by carefully opening the shut off valve.
- Watch pressure drop on the (VAG 1318).
After 10 minutes the pressure must not drop below a 3 bar decrease.
If the pressure drops further:
- Check the line connections for leaks.
If no fault is detected in the wiring:
- Fuel pump is faulty, replace the fuel delivery unit. Refer to --> [ Fuel Delivery Unit ] .