Releasing Pressure In High Pressure Area
Releasing Pressure in High Pressure Area
Special tools, testers and auxiliary items required
• Special Hook (3370)
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 120 bar) and a low-pressure section (approximately 6 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 the recommended pressure. The procedure for this is as follows.
High Fuel Pressure, Reducing
- Connect a vehicle diagnosis tester.
- 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
- Pry off the left cover on the instrument panel using (3370) - 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 (FP) 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 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 protective goggles and protective clothing when opening the fuel system.
• 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.
• If the high pressure system is not opened immediately, the pressure will increase because of post-heating.
• The ignition can no longer be switched on, otherwise the pressure will increase again.
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".