Procedure before opening fuel injection system high pressure area

• The fuel injection system is separated into a high-pressure section (max. approx. 120 bar) and a low-pressure section (approx. 6 bar).
• Before a component in the fuel injection system high pressure area is remove, the fuel pressure must definitely be reduced to a residual pressure of approx. 6 bar, as described in the following.

Special tools, testers and auxiliary items required 

• Vehicle diagnostic, testing, and information system VAS 5051

Work procedure 

• Start engine and run at idle speed.

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• Connect Vehicle Diagnosis, testing info. system VAS 5051.

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Display on VAS 5051 :

• Click on Vehicle Self-Diagnosis button.

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Display on VAS 5051 :

• In selection - 1  -, press vehicle system "01 - Engine electronics".
• Wait until next display appears.

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Display on VAS 5051 :

1 - Control module identification of engine control module (ECM)

• Click on → button.

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Display on VAS 5051 :

1 - Selection of diagnostic functions

• In selection - 1  -, click on diagnostic function "08 - Read measuring value block".

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Display on VAS 5051 :

• In button field - 2  -, press buttons 1 4 0 for "display group 140" and confirm entry by pressing Q button.

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Display on VAS 5051 :

• Check display for fuel pressure in fuel rail in display field - 3  -.

Example:

3 - 40.63 bar

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

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

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Display on VAS 5051 :

• Check indication in display field - 3  - :

• Fuel pressure in fuel rail must sink to approx. 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.

Faults are saved in ECM when electrical connectors are disconnected:

• Connect Vehicle Diagnosis, testing info. system VAS 5051.
• Start "Guided Functions" operating mode.
• Generate readiness code in ECM.