Releasing Pressure In High Pressure Area

Releasing Pressure in High Pressure Area

Special tools, testers and auxiliary items required

• Trim Removal Wedge (3409)

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 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 On Board Diagnostics (OBD).

- Select "Measured values".

- Select "Fuel pressure" from the list.

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






- Remove the fuse from the Fuel Pump (FP) control module (J538) with the engine idling.






• By removing the fuse, the voltage supply to terminal 30 for the FP control module is interrupted.

- Check the fuel pressure on the diagnostic system.

• 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 fuel come into contact with the 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".