Holding Pressure, Checking

Holding Pressure, Checking

Special tools, testers and auxiliary items required

• Pressure Tester (VAS 6550)

• Vehicle Diagnostic Tester

• The fuel pressure is OK and the pressure tester (VAS 6550) is still connected. Checking the fuel pressure, refer to => [ Fuel Pressure, Checking ] Fuel Pressure, Checking.






Test Sequence

- Activate the fuel pump with output diagnostic test mode to build fuel pressure.

- Read the fuel pressure on the pressure tester.

• The pressure may not fall more than 1 bar within 10 minutes.

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 immediately after the pressure has been reached. The pressure tester now shows the pressure on the fuel tank side.






If the pressure no longer drops now:

The fuel tank side is sealed. Look for leaks 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 all fuel hoses and fuel pipes on the engine if there is a lead on the engine side.

• A faulty fuel injector or a faulty high pressure pump on an FSI engine can cause leaks.

If the pressure drops again:

Check for the leak on the fuel tank side. Proceed as follows:

- Check the fuel line to the fuel tank for leaks.

If no malfunctions are found with the fuel line.

- Open the fuel delivery unit flange - 1 -.






- Make sure all hose connections - arrows - are connected.

If no malfunction can be found:

The pressure relief valve in the fuel delivery unit flange or pressure retention valve in the fuel pump leaks.

- Replace the flange with the fuel filter and then repeat the pressure retention test.

If there is still a leak:

- Replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit/Fuel Level Sensor ] Service and Repair.