Releasing Pressure In the High Pressure Area

Releasing Pressure in the High Pressure Area

There is a risk of injury because the fuel is under very high pressure.

• The fuel injection system is separated into a high-pressure section (maximum approximately 140 bar) and a low-pressure section (approximately 7 bar).

• Before opening the high pressure parts, for example removing the high pressure pump, fuel rail, fuel injectors, fuel pipes or fuel pressure sensor (G247) , fuel pressure in the high pressure area must be reduced to a residual pressure of approximately 7 bar. The procedure for this is as follows.

High Fuel Pressure, Reducing

- Connect a vehicle diagnosis tester.

- Start the engine and run at idle speed.

- Select "engine electronics" in OBD.

- Then select "Measured values" read out.

- Select measured value block 140.

- With the engine running in idle, the fuel pressure will be displayed in display field 3.

• Specified value: between 35 and 45 bar

- The fuse is located in the fuse holder in the right of the luggage compartment.

- Remove the right rear trim in the luggage compartment.

- With the engine running at idle, remove the fuse from the fuel pump control module (J538).






- Check the fuel pressure on the tester.

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

- Turn the 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).

Do not let the fuel come into contact with skin.

• The fuel lines will continue to be filled with fuel, but will no longer be under high pressure. Wear safety glasses and protective clothing when opening the fuel system.

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

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

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

Final Procedures

- Install the fuse.

- Erase the Diagnostic Trouble Code (DTC) memory and generate the readiness code in the Engine Control Module (ECM) in "Guided Functions".