Fuel Return Check Valve, Checking

Fuel Return Check Valve, Checking

The pressure retention valve in the fuel return maintains a residual pressure of approximately 10 bar.

The Piezo injectors need this control quantity for their function.

Special tools, testers and auxiliary items required

• Tester for Fuel Return System (VAS 6330)

• Follow the guidelines for a clean working environment when working on the fuel system. Refer to => [ Clean Working Conditions ] Clean Working Conditions.

• Always follow these rules before and during work.

- Remove engine cover. Refer to => [ Engine Cover ] Service and Repair.

- Before removing, clean the cylinder 1 return line connection using a commercially available detergent, for example.

- Dry the return line connection on cylinder 1.

- Cover the cylinder 1 return line connection with a cloth.

- Remove the return line connection on cylinder 1 by pushing the tabs downward and pulling the center part upward at the same time.

• Maintain clean working conditions. Dirt and contaminants must not enter the return line and the connection on the fuel injector.

- Connect the (VAS 6330) between the return connection on the fuel injector and the fuel supply hose.






- Start the engine.

- Check the pressure on the tester for fuel return system.

• Specified value: approximately 10 bar (145 psi)

If the specified value is not reached, replace the check valve.

Installing the Fuel Return Lines

- Replace the O-ring on the return line connections.

• Coat all the sealing rings with assembly oil or engine oil prior to installing.

- Carefully press the return line connections over the new sealing ring and onto the injector. The connection must engage audibly. Then press the release pin down carefully.

- Erase the Diagnostic Trouble Code (DTC) memory using a scan tool.

- Bleed the fuel system and check for leaks.