Fuel Tank: Service Precautions

Before Opening High Pressure Fuel Injection System


The fuel injection system is divided into a high pressure section (maximum approximately 120 bar) and a low pressure system (approximately 6 bar).

Before opening high pressure parts, e.g. removing high pressure pump, fuel rail, fuel injectors, fuel pipes, etc., reduce the fuel pressure in the high pressure area to a residual pressure of approximately 6 bar. The procedure for this is as follows.

High fuel pressure, reducing

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





- Start engine and run at idle speed.

- Select "engine electronics" in OBD.

- Then select "Measured values".

- Select "Fuel pressure" from the list.

- When the engine is at idle, fuel pressure between 30 and 40 bar is displayed.

- Pry off the cover - 1 - on the left of the instrument panel, for example using the trim removal wedge (3409) - arrow -.





- While the engine is idling, remove the fuse in the fuse holder inside the instrument panel on the driver side from the fuel pump control module (J538).





- Check fuel pressure.

• The fuel pressure decreases rapidly because the mechanical high pressure pump is no longer supplied with fuel from the transfer fuel pump (G6).

- Switch ignition off as soon as the fuel pressure drops to approximately 8 bar.

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


The fuel lines will continue to be filled with fuel, but will no longer be under high pressure. To open fuel system, wear protective eyewear and clothing to prevent injuries and contact with skin.

Before opening the high pressure system, place a cloth around the connection.

- After reducing fuel pressure, place a clean cloth around the connection and open the high pressure system immediately. Escaping fuel must be absorbed.

Perform the following steps are completing all work:

- Install fuse.

- Erase DTC memory and, using "Guided Fault Finding", generate the readiness code in the engine control module Vehicle Diagnosis, Testing and Information System (VAS 5051B).