Procedure That Must Be Performed Before Opening the High-Pressure Fuel Injection System - Pay Close Attention!

Procedure that must be performed before opening the high-pressure fuel injection system - Pay close attention!
^ The fuel injection system is separated into a high-pressure section (max. approximately 120 bar) and a low-pressure section (approximately 6 bar).
^ Before opening the high pressure section (e.g. to remove high pressure pump, fuel rail, fuel injectors or any other component or fuel line located in high pressure area of fuel injection system), fuel pressure in high pressure area must be dissipated in a defined manner to a residual pressure of approximately 6 bar. The procedure for this is as follows.

Special tools, testers and auxiliary items required





^ Vehicle diagnostic, testing, and information system VAS 5051B (VAS 5051 B version shown as example only)

Work procedure
- Start engine and run at idle speed.





- Connect Vehicle Diagnosis, testing info. system VAS 5051 B.





Display on VAS 5051 B:
- In selection - 1 -, press "On Board Diagnostic (OBD)" system and activate by pressing -> button.





Display on VAS 5051 B:
- In selection - 1 -, press "01 - Engine electronics" vehicle system and activate by pressing button.





Display on VAS 5051 B:
- In selection - 1 -, press "011 - Measured values" and activate by pressing -> button.





Display on VAS 5051 B:
- In button field - 1 -, press 1 4 0 buttons for "Display group 140" and confirm entry by pressing Q button.





Display on VAS 5051 B:
- Check read-out for fuel pressure in fuel rail in display field - 3 -.

Example:

3 - 40.63 bar





- Disconnect electrical connector - arrow - at Fuel Metering Valve 2 N402 on left high pressure pump.





- Disconnect electrical connector - arrow - at Fuel Metering Valve 2 N290 on right high pressure pump.





Display on VAS 5051 B:
- Check read-out in display field - 3 -

^ Fuel pressure in fuel rail must sink to approximately 6 bar.

- Switch off ignition.

The fuel rail will continue to be filled with fuel, but it will no longer be under high pressure.

Now components or lines can be opened. Lay a clean cloth around connection points and collect escaping fuel.

Final procedures
- Reconnect electrical harness connectors.
- In "Guided Functions" operating mode, generate readiness code for engine control module (ECM).