Fuel Pump, Checking
Fuel Pump, Checking
Special tools, testers and auxiliary items required
• Fuel injector pressure gauge (VAG 1318)
• pressure gauge adapter (VAG 1318/1)
• Adapter (VAG 1318/11)
• Hose adapter (VAG 1318/16)
• Adapter set (VAG 1318/17)
• Fuel line feed adapter (VAG 1318/23)
• Wrench (T10202)
• Remote control connection (VAG 1348/3A)
• Connector test set (VAG 1594C)
• Multi-meter (VAG 1715)
• Torque wrench (5-50 Nm) (VAG 1332)
• Voltage tester (VAG 1527B)
• Test instrument adapter/DSO (5 pin) (VAS 5565)
• Measuring container
=> [ Function and Voltage Supply ]
=> [ Fuel Pressure ]
=> [ Residual Pressure ]
=> [ Delivery Quantity ]
=> [ Current Draw ]
Function and Voltage Supply
• Battery voltage at least 11.5 V.
• Fuel pump fuse is OK.
• Fuel pump control module is OK.
• Low fuel pressure sensor is OK.
• Fuel pump function is checked via the output Diagnostic Test Mode (DTM).
- Connect the vehicle diagnosis, testing and information system (VAS 5051A) as follows:
- Connect the diagnostic cable - 2 - connector to the Data Link Connector (DLC) in the driver's footwell.
- Switch on the ignition.
- Press the buttons for "Vehicle Self-Diagnosis", "01 - Engine electronics" and "Output Diagnostic Test Mode (DTM)" on the display in succession.
- Press the right arrow button on display until the output Diagnostic Test Mode (DTM) of fuel pump electronics.
• The fuel pump must now accelerate slowly up to maximum RPM.
• Fuel pump runs quietly.
- Switch off the ignition.
If the Fuel Pump Does Not Start Up
- Remove the rear seat bench. Refer to
- Disconnect the electrical connector - arrow - from the fuel pump control module.
- Check the voltage supply between terminals - 1 and 6 - using the (VAG 1527B).
• Light Emitting Diode (LED) must light up.
LED does not light up:
- Locate and repair the open circuit in the wiring using the wiring diagrams.
LED lights up (voltage supply OK):
- Remove the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
- Check whether the electrical wires between the flange and the fuel pump are connected.
If no open circuits are found:
- Fuel pump is faulty, replace fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
Fuel Pressure
CAUTION!
The fuel supply line is under pressure. Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting, place a cloth around the connection point. Then release the pressure by disconnecting the connection.
- Disconnect the supply line - 2 - and catch any leaking fuel using a cloth.
• Press in the securing ring to disengage the fuel line.
- Install the (VAG 1318) with the (VAG 1318/17A).
- Open the shut off valve on the (VAG 1318).
- Switch the ignition on and off until the fuel pressure on the (VAG 1318) no longer rises.
- Read off the fuel pressure on the (VAG 1318).
• Specified value: 3.5 to 5.0 bar
If the fuel pressure is OK, check the residual pressure. Refer to => [ Residual Pressure ].
If the Specified Value is Exceeded
- Check the return line between the fuel filter and the fuel pump for kinks and blockage.
If no malfunction can be found:
- Pressure relief valve in the fuel filter is malfunctioning, replace the fuel filter.
If the Specified Value is Not Obtained
- Check the fuel pressure in front of the fuel filter. Connect the (VAG 1318) with the (VAG 1318/17) between the fuel filter and the fuel supply line.
- Open the shut off valve on the (VAG 1318). The lever points in the direction of flow.
- Start the engine and run at idle speed.
CAUTION!
The shut off valve must be closed slowly. At a fuel pressure of 8 bar, the shut off valve must be opened again immediately to prevent damage to pressure measuring device.
- Slowly close the shut off valve on the (VAG 1318). Pressure must increase to a min. 6.0 bar. If 6 bar is reached, open the shut off valve again immediately!
If the pressure has increased:
- Fuel pump is OK. Pressure relief valve in the fuel filter is malfunctioning, replace the fuel filter.
If the pressure does not increase:
- Fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
Residual Pressure
• Fuel pressure OK and the (VAG 1318) is still connected. Checking fuel pressure, refer to => [ Fuel Pressure ].
- Switch the ignition on and off until the fuel pressure on the (VAG 1318) no longer rises.
- Read off the fuel pressure on the (VAG 1318).
• Specified value: 3.5 to 5.0 bar.
- Watch the pressure drop on the (VAG 1318).
• After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the pressure drops further
- Switch the ignition on and off until the fuel pressure on the (VAG 1318) no longer rises.
- Immediately close the shut off valve on the (VAG 1318). Lever will then point in position - B -.
If Pressure Drops Again
- Check the fuel pipe to 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 Pressure No Longer Drops Now
- Check the fuel line to fuel filter for leaks.
If no malfunctions are found in the fuel line:
- Check the check valve in the fuel delivery unit. Connect the (VAG 1318) with the (VAG 1318/17) between the fuel filter and fuel supply line.
- Open the shut off valve on the (VAG 1318). The lever points in the direction of flow.
- Switch the ignition on and off until the fuel pressure on the (VAG 1318) no longer rises.
- Read off the fuel pressure on the (VAG 1318).
• Specified value: 3.5 to 5.0 bar.
- After the pressure has built up, immediately close the shut off valve on the (VAG 1318).
- Watch the pressure drop on the (VAG 1318).
• After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the pressure drops:
- Check 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:
- Pressure relief valve in the fuel filter is malfunctioning, replace the fuel filter.
Delivery Quantity
- Remove the rear seat bench. Refer to
- Remove the cover - 1 - with the fuel pump control module - 2 - from the fuel delivery unit.
- Disconnect the 5 pin electrical connector - arrow - from the fuel delivery unit.
- Connect the (VAS 5565) to the harness electrical connector and to the connector on the fuel delivery unit.
- Connect the (VAG 1348/3A) to the (VAS 5565) and to the battery positive terminal.
• This step allows the fuel pump to run when the engine is not running.
- Remove the fuel filler cap from fuel filler tube.
CAUTION!
The fuel supply line is under pressure. Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting, wrap a cloth around the connection point. Then release the pressure by disconnecting the connection.
- Disconnect the supply line - 2 - and catch any leaking fuel using a cloth.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAG 1318/23) and the (VAG 1318/17) to the (VAG 1318) and connect it to the fuel supply line.
- Install the (VAG 1318/16) to the (VAG 1318/11) on the (VAG 1318) and hold the other end in a measuring container.
- Close the shut off valve on the (VAG 1318). Lever will then point in position - B -.
CAUTION!
Danger of fuel spraying when opening the shut off valve! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold the container in front of the free connection of the (VAG 1318).
- Open the shut off valve on the (VAG 1318). Lever will point in direction of flow - A -.
- Operate the (VAG 1348/3A). Simultaneously, open the shut off valve slowly until 4 bar positive pressure is indicated on the (VAG 1318). From this point on do not move the position of the shut off lever.
- Empty the measuring container.
- Delivery rate of the fuel pump is dependent on battery voltage. Therefore, connect the (VAG 1715) to the vehicle's battery using adapter cables from the (VAG 1594C).
- Operate the (VAG 1348/3A) for 30 seconds and measure the battery voltage.
- Compare the quantity of fuel delivered with specification.
*) 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 approximately 580 cm3/30 s.
If the minimum delivery rate is not attained:
- Check the fuel lines for possible restrictions (kinks) or blockages.
If no malfunction can be found:
CAUTION!
The fuel supply line is under pressure. Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting, wrap a cloth around the connection point. Then release the pressure by carefully disconnecting the connection.
- Disconnect the supply hose - 1 - from fuel filter input.
- Connect the (VAG 1318) with the (VAG 1318/17) to the supply line.
- Resume testing the delivery quantity.
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 filter 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 sporadic loss of fuel supply:
- Check the fuel pump current draw. Refer to => [ Current Draw ].
Current Draw
- Switch off the ignition, switch off all electrical components and remove the ignition key.
- Remove the rear seat bench. Refer to
- Remove the cover - 1 - with the fuel pump control module - 2 - from the fuel delivery unit.
- Connect the current induction clamp - A - from the vehicle diagnosis, testing and information system (VAS 5051) or vehicle diagnosis and service system (VAS 5052) to the wire - B - to terminal 1 of the 5 pin electrical connector.
- 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, the test can also be performed during a road test, but a second person is required.
If the current draw is exceeded:
- Fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.