High Side Fuel Pressure, Reducing

High Side Fuel Pressure, Reducing

CAUTION!
The fuel injection system is separated into a high pressure side (maximum approximately 150 bar) and a low pressure side (approximately 7 bar).

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

Special tools, testers and auxiliary items required

• Vehicle diagnostic, testing, and information system (VAS 5051B)

- Connect the (VAS 5051B).





- Start the engine and run at idle speed.

- Select the "engine electronics" in On Board Diagnostics (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

- With the engine in idle, remove the fuse - in the relay/fuse carrier in the luggage compartment on the right side - for the fuel pump control module.





- Check the fuel pressure on the (VAS 5051B).

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

- Switch 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).

CAUTION!
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.

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

Final Procedures

- Reinstall the fuse - in the relay/fuse carrier in the luggage compartment on the right side - for the fuel pump control module.

- Erase the Diagnostic Trouble Code (DTC) memory and, using "Guided Fault Finding", generate the readiness code in the Engine Control Module (ECM) using the (VAS 5051B).