Fuel Pump, Checking
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, 3 Liter
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Pressure, Checking ]
=> [ Holding Pressure, Checking ]
=> [ Fuel Delivery Rate, Checking ]
=> [ Current Draw, Checking ]
Function and Voltage Supply, Checking
Conditions
• The battery voltage is at least 11.5 volts.
• The fuel pump control module fuse is OK
• The fuel pump control module is OK.
Test Sequence
• The output Diagnostic Test Mode (DTM) checks the fuel pump.
- Connect the vehicle diagnostic tester 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 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 - arrow - 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 - arrow -.
- Check the contacts on the connector and the fuel delivery unit for damage.
The fuel supply line is under pressure. Always wear protective eyewear 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 lines - 1 and 2 - from the flange.
• Press the lock rings to release the fuel lines.
- 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
• The output Diagnostic Test Mode (DTM) checks the fuel pressure.
The fuel supply line is under pressure. Always wear protective eyewear 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 using the output DTM 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. Refer to => [ Holding Pressure, Checking ].
If the Specified Value is Exceeded
- Check the return line between the fuel filter and the fuel pump for kinks or blockages.
If no malfunction can be found:
- Replace the fuel filter, the pressure relief valve inside the fuel filter is faulty.
If the Specified Value 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 pressure tester (VAS 6550) between the fuel filter and 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.
- Turn on the ignition and actuate the fuel pump using the output DTM.
- Close the shut off valve - A - while the fuel pump is running. The pressure must increase to a minimum of 7.0 bar. If 7.0 bar is reached, open the shut off valve again immediately!
If the Pressure Increased
- Replace the fuel filter, the fuel pump is OK but the pressure relief valve in the fuel filter is faulty.
If the Pressure Does Not Increase
- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.
Holding Pressure, Checking
• The fuel pressure is OK and the pressure tester (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 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 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 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 pipe leading to the fuel filter for leaks.
If no malfunctions are found with the fuel pipe:
- 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 pressure tester (VAS 6550) between the fuel filter and 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 output DTM to build the fuel pressure.
- Check the fuel pressure on the pressure tester.
• Specified value: 4.0 to 7.0 bar
- Close the shut off valve - A - once the pressure has increased.
- 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:
- The pressure retention 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:
- 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 Rate, 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 - arrow - 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 - arrow -.
- 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 the battery positive terminal in the engine compartment.
• This step allows the fuel pump to run when the engine is not running.
The fuel supply line is under pressure. Always wear protective eyewear 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. Always wear protective eyewear and protective clothing to prevent injuries and fuel from coming in contact with your skin. Hold the 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, 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 on 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 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:
The fuel supply line is under pressure. Always wear protective eyewear 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 supply line - arrow - from the fuel filter.
- Connect the pressure tester (VAS 6550) to the fuel supply line using the adapter (VAS 6550/1). Hold the other end of the adapter (VAS 6550/2) in the measuring container.
- Make sure the drain is closed and the shut off valves are open.
- 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.
- 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 the fuel strainer for contamination.
Only when up to now, no malfunction has been detected:
- Replace the 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. Refer to => [ Current Draw, Checking ].
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 - arrow - 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 - arrow -.
- 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. 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, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel Delivery Unit.