Before Opening High Pressure Fuel Injection System

WARNING: This page is about a different variant/trim than selected.

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

Special tools and workshop equipment required

Vehicle Diagnostic, Testing, and Information System VAS 5051B

Procedure

-- Turn off the ignition and connect the VAS 5051B to the Data Link Connector (DLC) using the diagnostic lead.

Fig 1: Locating Data Link Connector

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-- Start the engine and let it run at idle.

Display on VAS 5051B:

Fig 2: Display On VAS 5051B - Vehicle Self-Diagnosis Button

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-- Press the OBD button -1-.

Display on VAS 5051B:

Fig 3: Display On VAS 5051 - "01 - Engine Electronics"

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-- Press "engine electronics" listed in the menu -1- and then press the → button to continue.

Display on VAS 5051B:

Fig 4: Display On VAS 5051 - "006 - Basic Setting"

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-- Press the "measured values" listed in the menu -1- and then press the → button to continue.

Display on VAS 5051B:

Fig 5: Display On VAS 5051 - "Display Group 140"

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-- Press the 1 4 0 buttons in the button field -1- for "display group 140" and then press the Qt button to confirm.

Display on VAS 5051B:

Fig 6: Display On VAS 5051 - (42%, 39.76 Bar, 40.63 Bar, Inactive)

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-- Check read-out for fuel pressure in fuel rail in display field -3-.

A value of 35 to 45 bar is displayed when the engine is running at idle. The display shows the actual pressure in the fuel rail which is generated by the high pressure pump.

-- Remove the right luggage compartment side trim. Refer to Removal and Installation .

-- Remove the fuse 6 (on fuse panel F) -SF6- for the fuel pump control module -J538- in the fuse holder in the right of the luggage compartment.

Fig 7: Identifying Fuse Panel

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Display on VAS 5051B:

Fig 8: Display On VAS 5051 - (42%, 39.76 Bar, 40.63 Bar, Inactive)

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-- With the engine still running, check the fuel pressure in fuel system display -3- :

The fuel pressure decreases rapidly because the mechanical high pressure pump is no longer supplied with fuel by the electrical fuel pump.

-- Turn the ignition off as soon as the fuel pressure drops below 8 bar.

NOTE:

The fuel pressure must not drop below 6 bar, because otherwise the engine will shut off (risk of catalytic converter damage).

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

WARNING:

Do not let fuel come into contact with skin.

Wear protective eyewear and clothing when opening the fuel system.
Lay clean cloths around the connection before opening the high pressure area to collect any fuel that leaks out.

-- Loosen the wire at a connection immediately.

NOTE:

If the high pressure system is not opened immediately, the pressure will increase because of post-heating.

Final Procedures

-- Insert fuse 6 (on fuse panel F).

-- Connect the VAS 5051B while the ignition is switched off.

-- Start "Guided Functions" operating mode.

-- Generate the readiness code in the engine control module => .