Fuel Injection System

Before Opening High Pressure Fuel Injection System

The fuel injection system is separated into a high-pressure section (max. approximately 150 bar) and a low-pressure section (approximately 7 bar).

Before opening high pressure parts, for example removing high pressure pump, fuel rail, fuel injectors, fuel pipes or Fuel Pressure Sensor (G247), fuel pressure in high pressure area 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)

High fuel pressure, reducing

- Connect (VAS 5051B).





- Start 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

- With the engine idling, remove the fuse - 16 in the relay and fuse carrier in the E-box - for the Fuel Pump Control Module (J538). Current fuse.





- 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).

- 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).

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

Final procedures

- Re-install the - 16 relay and fuse carrier in E-box - for the Fuel Pump Control Module (J538).

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